For the price, it's a decent deal. You wouldn't be able to build a new system with that kind of budget, not without cutting too many corners. Gaming-wise, the performance will depend on the game, but in general you should be able to play at 1080p resolutions at medium to high quality settings & expect 50-60+ FPS (possibly higher quality and/or FPS depending on the game).
For 3-4 years? It won't stay at that level for that long...but then, a brand-new build won't necessarily stay there either -- compare the performance of a GTX 600/700 series card (released 4/3 years ago) to the performance of the current GTX 1000 series cards, for example, to see how much things can change in that length of time. However, it should be OK for at least another year at a minimum, & you could always do an inexpensive GPU upgrade down the road to extend its life. Or even save up your money so that, in a year or 2, you can look at getting a better all-around system.