I don't know if I have a least favourite set of games, but some were certainly frustrating and/or disappointing.
Halo Reach and Halo 4 both suffered from terribly implemented DLC. In the case of Reach, the maps were great but the playlists and rotation meant you hardly ever got to play on your shiny new maps with a full lobby of people more than a couple of times an evening - or if you did, it would be some ridiculous OTT variant like Infinite Fuel Rod, Infinite Jetpack Firefight. Halo 4's multiplayer was actually excellent (compared to the very unpolished campaign) but the DLC levels were the definition of lip-service. Spartan Ops was an embarassing exercise in visiting the same copy-pasted levels dozens of times and taking the story in silly directions.
Gears of War 3 and Judgment were both good games in their own right, but exemplars of why you never buy the Season Pass.
Rage was an enraging disappointment because of just how low it sets its sights. I felt mildly insulted as a player. They build a beautiful world, employ a sexy new game engine, and then... NPCs stand around with exclamation marks above their heads and dole out fetch quests. Fuck that noise. You promised me paradigm-destroying, open-world, hybrid gameplay; and what you delivered was a reskinned mash-up of the most safe and generic gameplay of last gen. Questing, crafting, upgrading weapons, tediously ticking boxes and making numbers on an offscreen Excel spreadsheet get bigger. No thank you.
Destiny also failed to be anything near to the groundbreaking Best Thing Ever that Bungie hyped it up to be. I remember when this game was called Phantasy Star Online. Wake me up when something actually innovative comes along.
Dead Island Riptide was a game I played through in a few hours flat, my face set in a permanent expression of bemused disbelief. How does something so sparse, so lacking in actual content, so utterly self-plagiaristic, get greenlighted? A lot of man-hours must have gone into this game, and every last one was wasted. The developers' keyboards must all have the Ctrl, C, and V keys worn down to nubs, such is the degree of copypasting evident here. NPCs. Environmental features. Enemies. It's one big Deja Vu trip where precisely nothing stands out. What an utter waste of a basically sound premise and central game mechanic. The paid-for DLC that gives your characters a slightly palette-swapped outfit, which you yourself will NEVER SEE in gameplay, is the icing on the cake.
Brink. I just never gelled with this one. The character design is singularly weird and uninspiring, and sets an offbeat tone that the rest of the straight-laced game fails to capture.
Timeshift - Nice idea, shame about the game.
Tomb Raider Reboot - sorry Lara, but dragging your bony, complaining butt over every jagged rock, down every waterfall and off every cliff in sight is just tedious. Making your protagonist the damsel just doesn't work.
Assassin's Creed Brotherhood - not a baaaad game, but this definitely marks the point where Ubisoft decided "right, we're milking this cow until dust comes out of the udders".
Sonic the Hedgehog 4 - this is NOT a sequel and doesn't deserve the number 4 next to its name. "Glossy but slightly Uncanny-Valley HD remix of the best levels from Sonic 1 and 2" would have been a much more accurate name.