Sonic the Hedgehog 3D is a free fan game about a famous SEGA mascot, Sonic, and it is made on Build Engine with additional EDuke 32 port. The game was inspired by two classic Sonic series: Mega Drive/Genesis and Sonic Adventure series.
it's just the fact that you have 4 characters with their own abilities and full 3d inviroments, models and the gameplay is addicting and i have beaten it, gotten all chaos emeralds, beaten all stages twice with every character. my only problem with the game is that is pretty short because well so far it is only a v 0.3 but so far so good