Decimation tools generally create crappy meshes. OK for organic static things, like rocks or the like. Also good for reducing a super-highpoly sculpt into a semi-highpoly that's easier to bake with. But bad for mechanical or built objects, or any mesh that needs to deform for animation (like characters). If you have a…
Yeah these are all too high-poly to work in your typical real-time in-game scenarios. One of the best ways to get a grip on polygonal density is to play games. No kidding! Play a game that has graphics you like, and spend a lot of time just looking at the models. Get up close, look at it from multiple angles, try to…