Well..for ten bucks it's pretty dang good. Here is a video to back up my claim: http://www.youtube.com/watch?v=dapozJPTTiA
there are plenty more videos to watch of that quality out there...
there are thousands of designs out there like that.. and you can make designs like that too with a bit of practice and a good head on your shoulders
As for activity, i doubt it will dry up, but that said the fun of the game without the community is worth at least the $10 in my opinion.
there are currently around 30 or so solid members on the forum who are all pretty much awesome people i doubt that will fluctuate much :D also there are a number of competitions and level sets to join and play.
the actual game seems to have around 85 people online at a time, there are usually a fair amount of new levels created per day as well.
If you check the other forum topics you will see there is enough activity to enjoy your stay haha.
if you are putting ten bucks into your new account im sure nobody will mind
As for FC2, i do not believe the payment here carries over...that one has a decent community too, but i like this one better..i'd suggest checking that one out as well.
Hope this helps!