1. How many servers/players are usually online?
At the time of this writing, there are 65 servers and 215 people playing. That's probably a decent average, but new people are joining daily, and I play with people who have been around from the start, so players don't quit often. I'll always find a server to join, or start my own and have friends join it.
2. I have a really old version (a year and a half, I think) of Return to Blockland, will that do the same stuff as the new blockland?
3. Does the version of RTB that I have do mods and maps, like bombs and weapons?
5. What is the difference between RTB and Blockland?
RTB did have a lot of neat stuff, mainly because Lego hadn't caught onto it, and it wasn't commercial. So, people could go wild and release anything they wanted. However, retail brings things into a much better package. In my opinion, the interface and tools are far better, and new tools are released fairly often from players wanting a bit more. The brick variety is smaller, but it's still a great selection. There are tons of addons, maps, decals and all sorts on retail and most importantly, it's the main version, so more people build more things. Things can only get better for retail, where as RTB stays the same.
4. Do I have to pay each time a new version comes out?
No, one time payment.
6. Is it worth the $20?
Yes, it's not much, and although I don't play daily, the mature side of the community and the sheer limitless possibilities are well worth the money.