I know we're rather pass the mod promotion part of this thread, but here we go. LFR is a good mod and you should give it a try. You got some pretty unique features to go with the interesting lore, which make for great community fortress stories. I myself mostly play for the features it has and will get when the new DF version is up. It gets pretty hard in the late game too, with all the voidwalker destroyers blasting around with their high tech weaponry. I'd say it's one of the few harder mods, and I've been playing since 40d. FPS wise, LFR has a simplified clothing feature (optional) where your invaders and dwarves won't be scattering socks and other unimportant clothes around draining your FPS, yet they will still have almost full clothing coverage and the benefits that brings.
I can vouch for Intensifying Mod & Masterwork for the vanilla feeling and FPS save, Corrosion and Ponies for awesome total conversion, FD for the intense difficulty and Genesis, Dig Deeper, Regen and Civ Forge for the diversity in races and items. But I think LFR is my top mod, as it combines all of the above (other than the staying true to vanilla) - difficulty, diversity in races and items, total conversion feeling*.
(*with the tech tree it brings, LFR's definitely not just adding more items and races)
Anyway, that's my take on this.