Where should you go if you want a fulfilling Sci Fi story? Star Control 2. Or if you recently picked up the Mass Effect Trilogy for a good deal and decide to replay the series. Some have claimed that the original hasn't aged well and it hasn't because Mass Effect 2 outdid it in almost every aspect.
Every aspect except the Mako Tank above. I love this tank. It rolls over everything. Some of the best parts of this game were blindly exploring planets trying to gauge whether or not you can scale a cliff face. I must be the video game version of a red neck, while I'm searching for Saren I stop on an abandoned planet and go muddin.
Serious Sam: The First Encounter is a masterpiece. Well, a budget game when it was released that still manages to be notable almost 15 years later. The entire game is frantically paced and self aware. The secrets left all over the levels are much more involved than "hidden item closets" by giving stupid/humorous messages, messing with gravity, and may have elaborate optional encounters that are on par with the main game. Skip the HD remake, it didn't add much to the experience.
Play what you like. Like what you play. If you feel something is missing in an experience seek out what you crave. As long as it's legal and doesn't make you look like too much of a dirtbag.
