I haven't played Fallout 3 before.
I haven't played Fallout 3 before.
I doubt you'll have sufficient time to enjoy Fallout 3 before Fallout 4 arrives. The narrative isn't overly long, but with DLC and side missions it can become quite lengthy. Fortunately, Fallout 4 isn't heavily reliant on Fallout 3, so you shouldn't face too much trouble. I still plan to play both games and their expansions.
I haven't played 1&2, but most fans say FO3 skips a lot of the original content. If you love 1&2, you might feel a bit disappointed with FO3. However, many issues can be fixed with mods. You could enjoy it before FO4 if you don’t intend to play that later. It’s probably going to have bugs and need fixes from modders, making it less polished around the time of release. It should improve a bit in about six months. Given Bethesda's recent work, you probably won't find much excitement from this one either. So it might be wiser to wait for FO4. Try playing a modded version of FO3. Also, New Vegas is a better balance and has a stronger story, and since it was made by the original developers, it fits more naturally into the FO universe.
Use plenty of mods to fix the old-school vibe. Skyrim looks much smoother compared to New Vegas or 3.