For Xbox users who aren't interested in having access to a ton of Game Pass titles and are mostly just looking to play a few favourites online, Xbox Game Pass Essential is the best and most affordable option (£6.99/€8.99 per month, though you can get it cheaper if you buy multiple months at once) to do so.
But even with Essentials, you get a pretty substantial collection of around 60 games to enjoy, including Deep Rock Galactic, Fallout 4, and Stardew Valley. TrueAchievements has now noted that more games have been added to the list (an official announcement should be coming soon, but we've verified that this is correct), namely:
Blinx: The Time Sweeper
Iron Brigade
Jetpac Refuelled
Kameo: Elements of Power
Massive Chalice
Max: The Curse of Brotherhood
Neon Abyss
Perfect Dark Zero
Stacking
We highly recommend checking out Rare's Kameo: Elements of Power and Stacking from Double Fine, both of which are top-notch games. For purely academic purposes, Blinx: The Time Sweeper is also interesting (a rather subpar platformer, but Blinx was considered by many to be Microsoft's equivalent of Crash, Mario, and Sonic), as is Perfect Dark Zero, which is the final game featuring Joanna Dark, perhaps forever.