JDR and others you must absolutely try all of Pucemoose's amazing quests/adventures which are more like expansion packs then mods, though there are gameplay element mods, weapons and all kinds of stuff in addition to some of the most memorable gameplay adventures and wonderful experiences that mesh the usually static adventure puzzles, and stories with the spontaniaty of the wasteland. I highly also recommend playing them in order. I finally made a run of them all in the prior to months after enjoying the first last year. Mr Manchesters and Perchance to Dream were 2 of my favourites and his latest Mantis which I haven't done the "Mothership Zeta" rework yet is great, especially for the radio station you can unlock with some really old gems.
http://www.fallout3nexus.com/modules/members/index.php?id=137055
I would honestly have paid full price easily for fallout 3 just for these free "mods"
the weapons are great and Manchester has probably the best party character ever in an RPG, a crafty turret that you can teach to do things after you build and continuous upgrade it and find out more of its mysteries, it be comes a fun mechanic that can also save your ass as it gets along. So far i'ts learned over 30 different weapon loadouts and I still haven't maxed it out. Be warned it will be rather weak though in the beginning against tough opponents especially melee ones.
Puce brought a much needed human element with his explorations of "the little guy" in all of his texts/quests that was greatly missing from fallout 3, in addition to all of his construction, logic and other minigames, and of course upgradeable and "learning" weapons. There's even a rather relaxing fishing minigame in To Sleep - Perchance to Dream.
other than that the gypsy outfit/npc mod and one weather mod which adds in some sometimes appropriate irradiation rain which goes well with Point Lookout, and it can also be heard faintly inside.