I have been playing a lot with the Eldar fleet lately.
I want to share some of what I have found about the different ships.
Of the cruisers, I find the Eclipse to be the most useful of the two. Its launch bays and twin prow pulsar lances can take on any opponent up to and including a battleship with its speed and maneuverability. Its strengths are its launch bays and pulsar lances, and its high maneuverability and ability to move twice per turn. Its weaknesses are the same as all Eldar ships - only a 4+ armour and only 6 hits. Also, you must plan every move to make use of the solar winds.
The Shadow class, its strengths are its four prow torpedoes and its twelve prow weapons batteries, which can knock down shields and do damage and then run away in the same turn. Its weaknesses are the same as the Eclipse.
All of the escorts are well armed for their size.
The Hellebore carries one pulsar lance, two keel torpedoes, and one prow weapons batteries. This ship can go on special orders for one turn and still fire all of its weapons. It is great for hit and run attacks. Its weakness is only one hit, and it suffers from the other weaknesses that the cruisers suffer from.
The Aconite, the prow weapons batteries can be very useful in conjunction with other ships, but this ship must be used in a support role for other ships. In a squadron, the Aconite can be awesome. Take four Aconites and you have 20 weapons batteries for only 260 points. This is the way to use the Aconite, in squadrons, but remember, plan your moves to use the solar wind, and this can be more difficult with multiple ships. A squadron of these are the perfect backup to a squadron of Hellebores.
The Nightshade class destroyer, this ship can become a total nightmare for your enemy! In squadrons of five or six ships in base to base contact, they can launch a huge wave of torpedoes, and they have their prow weapon battery for backup. Another great ship for backing up your Hellebores when you have these ships in squadrons. You can pull a leap-frog maneuver with these: Jump your Hellebores up, and fire your torpedoes, then jump back. Then jump your Nightshades up and fire their torpedoes while the Hellebores reload.
Hemlock, what can I say about this ship? This is one awesome weapon! For that matter, that's what it is - a flying weapon. A squadron of these, six strong, can destroy a battleship in no time at all. But remember, they have the weaknesses of all Eldar ships, so avoid getting them hit, and plan your moves to take the most advantage of the solar winds.
You must avoid getting caught in a barrage of enemy weapon batteries. These are the bane of the Eldar fleet. Also, be careful of blast markers and space debris, as you have no shields. The holofield only makes it hard for the enemy to hit you, it doesn't give any protection against physical damage.
One of my favorite tactics is to use a squadron of six Nightshades supported by six Hemlocks, and use the Hemlocks to protect the Nightshades when they reload. The Eldar ships are the perfect ships to use torpedo tactics with. They are fast, and they are very maneuverable, they can move anytime they wish as long as they have the use of the solar winds. They also have a +1 Ld. They have the pulsar lance that hits on a 4+ and can get as many as three shots per turn as long as they keep hitting. Eldar weapons batteries count all targets as closing, which means they will get maximum shots no matter which direction the enemy is going. The Eldar's torpedoes are only hit by turrets on a roll of 6, instead of the 4+ of other torpedoes, plus you can reroll to hit if you miss on the first attempt.
The Eldar fleet is for the person who wishes to use cunning and maneuvers to win. They are for the planner. They are not for the admiral who wishes to force his way through and attempt to win on brute force. Add to this the fact that the Eldar ships are some of the most beautiful models when painted correctly, and they make for a great fleet for the admiral who wants more than what the Imperial or Chaos fleets can give them. The Eldar take more effort in painting and in planning tactics, but they are definitely worth it. The satisfaction of seeing the look on your opponent's face when your Eldar come swooping in and damaging his fleet while always eluding the majority of his fire is definitely a rush.