1) Banjo Kazooie Nuts & Bolts: sorely underappreciated, brilliant if you want to get creative and has all of the charm you'd expect from a Rare game. Too many dismissed it without even trying it. (A PC port would be appreciated)
2) Prey: the new one I mean, the old one was great back in the day, but has aged terribly, (would love the cancelled sequel to that as well). Sad it didn't sell enough for a sequel and they are making a coop vampire game instead...
3) Space Marine: Unfortunately the publisher went under and it also didn't sell as much as hoped. Loved it more than any Gears sequel myself. Still living in hope they make a sequel! Need more quality 40K games!