I used to play woodsball/scenario ball because that's what I had access to. For me it was all about MILSIM, so moving from paintball to airsoft was easy-peasy.
I'm not going back though. To be honest, I hate getting messy from paint and the masks are bulky and annoying to aim with. Paintball is not as good for MILSIM as airsoft either. Furthermore, and as already stated, paint is expensive and goes bad quickly.
As for what you should expect: expect people to be more serious about MILSIM. Depending on what kind of paintball you played, players will be more serious about real-world tactics, terms, handsignals, etc. An example: recently I played a game with one of my friends who had never played airsoft but had some paintball experience. He was kind of confused at first when I told him to "provide point fire on the number 2 window". To me (and a lot of more experienced airsofters) this comes almost naturally, but people who are new to it might need to have it explained.
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