The old Eldar and shields debate. Well, Eldar shield technology is supposed to be much better than that of the Imperium. According to fluff they look down on the crudity of Imperial shields, much like the Imperium would with Orks. Wave Serpents are supposed to have shielding for example (though it is poorly represented in 40k). Eldar have shields on their Titans and massive vehicles (I'm pretty sure this is reflected to some degree in Epic rules). In 40k rules this is often reflected as a flat save, rather than absorbed hits (much like Necrons get in BFG). For a BFG example of Eldar shielding, the resilience of Eldar fighters is due in part to their shields.
The biggest problem is that those that made the rules for Eldar ships in the first place took on board 2 things about Eldar. 1) Their propensity to try to avoid fire rather than resist it. 2) The fact that most often Eldar shield, though putatively better, have been represented as saves rather than absorbed hits in GW game systems.
There are a couple of things wrong with this. Firstly, it would be utterly essential to have shields in space. You can't "fool" a swarm of micrometeoroids into not hitting you. Or a good deal of other celestial phenomena for that matter. This is particularly salient for the Eldar who spend a tremendous amount of time hiding in just that sort of terrain.
Secondly, shields in BFG are the best defence in the game. What they do very very well is protect you from incidental fire. A couple of hits against an IN cruiser is worthless. Not so an Eldar or Necron cruiser. They require that the enemy focus his fire or risk wasting a good deal of it. This then makes brace decisions easy as well as meaning that further fire will likely be reduced by BM interference. A Necron player will take less overall damage from a lot of focussed fire due to his save, but against incidental fire it is much worse than shields, so the opponent can split his fire. The Necron player will take the same number of hits as if they were focused, but since it's spread out the Necron player won't get the same benefit for bracing, unless he braces all ships, in which case he loses a lot more than a player with shields would. Not to mention the fact that BMs don't get placed to screw with gunnery.
So shields > other defences. Which makes me wonder why the Eldar are so disdainful of such an effective defence. Also, when you read the description of imperial void shields they get overloaded. Eldar shields aren't supposed to (hence in most systems they're represented by a save rather than absorbed hits). I think that normal BFG shields should have had a chance of coming back up when out of BM contact, rather than automatically coming up (if that test is failed, place a BM in contact for each shield that failed). Eldar shields on the other hand should be like shields are currently. Automatically come back.
But since that's not how it is, I put forward regenerative shielding.
Note (horizon): the regenerative shields I just put forward are somewhat different to my original proposal. Originally they were supposed to get a regenerate test against each point of incoming fire (much like a brace save for shields) which if continued to be passed would result in the hit being completely ignored. It would take a number of fails equal to the number of shields to drop them all. So a BB with 3 shields at 4+ save would roll 3 dice against incoming hits. Any that came up 4+ would absorb a hit and keep rolling to absorb more hits. Only when you'd failed all 3 shields saves at least once would all the shields be down (failed saves absorb a hit too). So this rule was a little fiddly in that you kept having to roll dice and also powerful in that it could end up giving quite a lot of shields in the end.
In the proposal I mention above you would take hits exactly as a normally shielded ship except that when the enemy ship/squadron has finished shooting you roll 1d6 per point of shield strength. For each 5+ you remove a BM from base contact (essentially getting back 1 shield). Then the attacking player chooses his next ship/squadron to fire with and continues his turn. So if a BB had 3 shields it would like get back 1 for successive firing. This process would be repeated each time an Eldar ship is the target of fire, possibly getting back more shields. Overall this would amount to more protection when looking at multiple squadrons focussing fire on the one Eldar ship (much like Necrons flat save would do), keep incidental protection up (1 or 2 hits won't cut it!) while making the Eldar ship slightly weaker than its IN counterpart as far as a single squadron is concerned (they'd only need to get through 3 shields, not 4).
Besides, it's Harlequins that depend most on holotech, not CE or CWE! For DE a clear demonstration of their shield tech is the 40 shadowfield, which has been bastardised in BFG.