Whilst very good, FOOK goes heavily against Fallout lure. Eg you've got modern assault rifles and like coming out of the arse.
XFO is a highly regarded balance mod and Martigen's Mutant Mod is also (often used in combination with either one or both of the aforementioned).
I've most just used visual enhancement mods (eg high res textures) and small mods that tweak a few aspects of gameplay, like the shitty vanilla repair system, the range from which you can activate VATS and the stupidly high rate at which weapons degrade.
Some of the mods that I use:-
Off the top of my head, Darn's UI and Fallout 3 Unofficial Patch (F3UP) are essential installs. Also Fallout Mod Manager (FOMM) by Timeslip and Fallout Script Extender (FOSE) are essential downloads.-The texture packs by NMC.
4Aces weapon and armour textures and texmeshes + his environment texmesh pack (his massive several GB hi res pack incorporates NMC's packs)
-EVE - Energy Visuals Enhanced by Weijiesen
-Weijiesen's high res power armours
CptJoker's texture packs for clutter and the like. Better Booze, cigarette mega pack, enhanced night sky, etc.
Then just search Fallout3nexus for more, such as hi res skill books, VaultTech lunchboxes, Nuka Cola machines and bottles, etc.
Enhanced Weather - Snow and Rain is awesome.
Also Fellout. Removes the green hue that everything has.
Once you've installed all of your mods, I recommend creating a merged patch in FO3Edit, put it the very bottom of your load order in FOMM. This gives you increased stability, because mod incompatibilities can make the game crash. You have to make a new one every time that you install or uninstall a new mod that uses an ESP.
Also patching your ESPs by running FO3Edit in MasterUpdate mode decreases incompatibility.
In your load order put any ESMs at the very top, with Fallout3.esm first and any DLCs that you have purchased directly after it. The U3FP ESPs should proceed directly after your ESMs.
Small gameplay tweak mods that I really like are cross-repair mods, Repair Rethought Reborn being the best. I also use one that extends the range of VATS, perfectly suited for use with the sniper rifles and the Gauss Rifle (from Operation: Anchorage).
Sniper Rifle aiming fix, scope aiming is totally off-centre and broken in vanilla FO3.