This is actually easier than the previous mission. The attacks on your base don't start so early, and while you have a big fight in the end, you'll have way more space to maneuver instead of attacking a funnel kill zone.
The map is divided by a river and the only bridge is closed, so the mission as two distinct parts. First of all, turtle. Take the two Strategic Points right in your base and don't go out. This way you can build and tech up for quite a while. Make several generators, tech toward vehicles as soon as you can. You also need one missile squad in case you get tank-rushed before that, and some anti-infantry (like one flamer squad and one heavy bolter squad). Build turrets.
You will eventually be attacked from all directions except below, but the big ones (with vehicles) come from the left; only 1–2 infantry squads at a time from the other entrances. In addition, there will be the Avatar, who's not really so tough; he will run away after receiving surprisingly light damage. Let him go until you think you can finish him, then rush after him for the kill (don't do this when he runs west, as you'll run into tanks and stuff - wait for him to go north or east). When you can spare the troops (say one Dread and one squad), go get the SP on your right. Also get the Relic; it's unclaimed. These will be left almost completely alone. When you get the left SP it will draw tank attacks and the like so don't go there until you can handle it.
When you have two lascannon Predators, you should take out the left side (minor Eldar base, Slag Deposit, Relic) without trying. Then send Skull Probes to scout the main base. Note that you can attack it from behind if you want, right where the production buildings are. They don't have decent anti-vehicle so Preds and Dreads will own them. Then clean your side of the river (lone squads will keep appearing at certain locations throughout the mission, you can't stop those). Before taking the gate-opening Strategic Point, stop.
When you take the SP and open the bridge, two things happen: you will be rushed by swarms of Eldar and two builders will appear on your side of the river. For the latter, have a squad/vehicle ready to search your side (the builders may have been at the square and crater south of your bottom Relic and SP) until you find two Bonesingers. For the former, have a good main force in position to hold the bridge when it opens. Use four Predators lined to block the bridge with four Dreadnoughts ready to drop when needed and heavy-weapon infantry behind the tanks. This is the first time you can get Terminators so maybe you want to try out those; have one Terminator Squad with assault cannons and one Assault Terminator Squad. Attach your commanders to these. One Assault Marine Squad may also be useful.
When you have this set up, open the bridge and start pushing forward. If they bring lots of anti-infantry units to the front then lead with vehicles and vice versa. Drop Dreads where needed, teleport Assault Terminators in and out, use your special abilities liberally (especially Orbital Bombardment). Build a secondary base at the other end of the bridge to replace any units you (may) lose. When your main force advances by the main street, you can take one Tactical Squad and one Assault Squad south to take out a couple of Webway Gates.
There is some heavy fighting in this final part, but you shouldn't have major difficulties. Just use your units logically - who should be shooting at what, who do you move up front to absorb that, and so forth. Press on slow and steady, and soon your tanks will be shooting at their production buildings. You will win the mission when you can move to the dig site.
The next mission is The Chapel.
If you don't mind being cheap, 5-10 Land Speeders with a similar amount of Assault Marine Squads jumped over the river can reportedly clear out the north side before you even open the bridge (on any difficulty level). It may not be as satisfying as winning "like you were supposed to", though.
Or you can try as i did it, call only Dreads from the Machine Cult. Right after you open the bridge, send 3-4 Dreads south-east of your primary base, there will be an Eldar base, if you do not destroy that base, you will be overwhelmed by the Eldar that come from there, those Dreads will make short work of that base. After you secured your side of the map, send all the Dreads to the other side, and just take them trough anything the Eldar throw at you, and that final battle will be a piece of cake with the Dreads, 5-6 Dreads will probably do it, but i sent them all to be sure nothing goes wrong. One little detail i forgot to mention, upgrade the Dreads with Twin-Linked Lascannon, so they can destroy the enemy vehicles and buildings fast, infrantry can't really hurt the Dreads so you won't need Assault Cannons.
Another strategy is to simply turtle until you gain the Orbital Relay, then deep strike a dreadnaught to the key, which is visible to you. When you can see more, deepstrike two more. They should make short work of the Eldar and their base.
Second Alternative Edit
As a slight variation that will not require the player to capture the bridge, nor to destroy any Eldar bases, and focus only on taking the objective (the Key). This involves infiltrating some Scouts across the river to observe the target area, then performing a full-scale drop pod assault directly on the objective.
The first step is to get a squad of Scouts across the river, which you can do by using an Orbital Relay to Deep Strike a squad of Scouts onto the northern side of the river. Deep Strikes can only be performed in areas with direct vision, so to accomplish this, just use an Assault Squad (or a Land Speeder) to jump across the river and gain vision of the northern riverbank. Immediately jump the Assault Marines/Land Speeder back to the southern riverbank before they attract any attention from patrols. The Scouts should Infiltrate immediately after exiting the drop pod, and they can then sneak their way to the objective (being careful to avoid enemy commanders and any other infiltration-detectors).
Once the Scouts have vision of the Key and the Eldar units surrounding it, load the Orbital Relay with your attacking force. Each unit must be carefully chosen specifically to tie up and counter the Eldar force guarding the key.
- Wraithlords can be tied up using one Dreadnought apiece; it is better to leave your Dreadnoughts un-upgraded (keep both Dreadnought power fists), as they won't have much shooting to do.
- Space Marine squads can generally neutralize the Dark Reaper squads in close combat (set the Space Marines to aggressive melee orders before loading them into the Relay, and they will immediately seek out the nearest Dark Reaper squad for close combat). It is possible to tie up two closely-spaced squads of Dark Reapers with a single full-sized Space Marine squad, but this requires very careful positioning. Once each squad has finished beating up their assigned Dark Reapers, switch them back to Hold Position/Ranged Stance, and turn their heavy weapons on other targets.
- Taking Terminators is not strictly necessary, but their toughness and firepower will help. More importantly, since they can teleport into battle from a separate facility (load them into the Chapel Barracks instead of Orbital Relay), they can be sent in as additional units. If you bring them, you may either use them to sweep the Dark Reapers more quickly with storm bolters and assault cannons, or you may have them assist the Dreadnoughts with meleeing the Wraithlords to death (note that vanilla DoW Terminator power fists do respectable damage against vehicles, just like in WH40k canon). This versatility will allow them to transition between attacking any and all Eldar target types.
- Attach the Force Commander and Librarian to any Deep Striking units of your choice, but preferably attached to units that will land in the center of the battle. Immediately after exiting their drop pods, you may detach them so that they can tie up two separate enemy squads if needed. Use every ability at your disposal to reduce (or even fully prevent) casualties on your men. Use Battle Cry to speed up the killing, trigger an Orbital Bombardment on one section of the battle there is room, cast Smite immediately on the largest concentration of Dark Reapers, Weaken Resolve on another Dark Reaper squad, and most importantly, use Word of the Emperor as soon as one of your squads is about to start losing members.
Once committed, you must very rapidly Deep Strike all your units, with your entire force landing roughly in a space of one second or less (hotkey your Orbital Relay and Chapel Barracks). In vanilla DoW1, Drop Pods also cause disruption knockback on landing, allowing the Eldar no chance to react. On aggressive stance, most of your units should automatically attack their correct targets based on drop pod positioning, allowing you to focus on quickly micro-ing your two HQ units.
Note: When the game is Paused in single-player, orders can still be issued. Most notably, you can mark locations for your Drop Pods (and Terminator teleport attacks) when Paused, which will result in all of the drop pods hitting the ground at the same time.
With proper pre-planning and use of abilities, it is possible to drop out of the sky and immediately wipe out the Eldar guarding the Key in seconds, without taking a single casualty.The remainder of the Eldar forces can be ignored. The mission will end successfully immediately, once the top of the hill is secured.