There is too many...
For example, I already played it for 40 hours when it came out without any mods, loved it, but stopped playing after reaching level 20 without finishing...decided to wait for mods and DLC.
Now, 3 DLCs are out, but two more are on their way, and there is so many other mods that are game enhancing..
but then, patch 1.1 broke VATS system, it lags now (it did not lag in 1.0) and it is still not fixed, even with patch 1.5 : /
So basically, I am now waiting for them to :
1)fix VATS (essential, I hate waiting before every shot for percentages to appear)
2)release all the DLC
3)fix those (because they will be broken, it is Bethesda after all)
4)update all the essential mods and texture packs to be compatible with the patches and DLC
So basically I am probably gonna wait another year.