So, I just had a long, epic 2v2 with Lothlorien, I'll post the replay in the replays section. There are many big issues that have come to bear, it seems that Lothlorien really are one of the weakest factions in late game. I'll list my points below.
Firstly, Lothlorien are not only weak against cavalry of Gondor, but also tower guard spam. Over and over again, he would hit me with massive tower guard armies that just, wouldn't, freaking, die. Even with a bunch of galadhrim with silverthorns, and caras galadhon guardians, I just wasn't dealing enough damage, and the conflict would destroy both of out armies. I highly recommend increasing the damage of silverthorn arrows, they seem rather weak right now. After all, Lorien is supposed to be the highest damage archer faction, to make up for their lack of heavy armor.
Secondly, Elves really have no good counter against siege positioned behind an enemy army. He sniped me with these all game, killing my heroes and huge clumps of my army, and I could not really do much of anything about it. For those of you who say that ents could counter, he had fire stones. 1 shot and the ent would be lit up and run off and die. I suppose Beornings could be used to counter, but I was not getting them because they cannot effectively counter tower guards, and additionally the other opponent was Rohan, who could just trample them to death with no problem. Another point in regards to Ents is that they cost too many command points, I can't see them being worth more than 45 in relation to their resource cost. How many command points do trolls cost? They should be identical.
Thirdly, Galadriel takes WAY too long to level up, I wasn't able to make use of her level 10 invincibility until the last 10 minutes of the game, at which point we had already basically lost. She is also incredibly vulnerable to siege and arrows, I think that she should perhaps receive a little bit of a buff in resistance to ranged, considering how expensive she is. Also, glance in the mirror is utterly useless, if the negative effect were removed it would be useful.
Fourth, Palace Guards aren't really very great. The damage is nice, but honestly it isn't enough. They cannot survive in prolonged melee against much of anything. I think that the palace guards alone, due to their heavily armored look, should be the only unit able to research heavy armor as a default upgrade, and they should have a formation better than porcupine formation, something that gives some armor.
Fifth, the Elves late game powers aren't that great. The Rain doesn't do much damage to late game upgraded armies, and the boat can be overpowered by other powers, such as army of the dead. I think they should both be buffed, the boat by a small amount, the rain by a fair amount. Also, even with the spell which reduces cooldown times, my spells seemed to be taking a very long time to recharge. Cooldowns should perhaps receive a second look.
Sixth, the elves don't really have any great mass slayer heroes. The only decent mass slayer power is Legolas' Arrow Wind, which he doesn't get until level 10. I'm not really sure how to address this, maybe improve Grimbeorns powers? I also think he's a little too expensive, he's worth maybe at most 2000.
That's the majority of the points I can think of right now, I will post the replay of the game I'm talking about in the replays section for your enjoyment, and I'm sure I will have about 10 million people pointing out mistakes I made in game
To sum it up, I would call Lorien the 2nd weakest faction in late game with the current balance, behind Rohan. They are especially weak against Gondor, who have the perfect roster to clean them up, either with tower guard spam or cavalry.