Broken Base: This game was hated by a lot of the series' older fans when it came out, due to the graphics, controls, plot, rehashes, retcons and frequent errors (in the PC version at least). But conversely a lot of people grew up with this (and possibly Curse) as the only Monkey Island games they knew and so recall it fondly. By the time Tales Of Monkey Island came out, the demographic had shifted, and Escape was generally considered in a more positive light.
Still, even if you only compare it to Curse, it's disappointing, especially given that Curse was arguably the best game of the series, with the same or better sense of humor and vastly superior graphics.
Contested Sequel: Widely considered to be the weakest game in the series. The Retcon as to Toothrot's true identity doesn't help.
Disappointing Last Level: The player is stranded on Monkey Island for the last third (almost half) of the game to fight an annoying rock-paper-scissors style fighting minigame and have tons of exposition and retcons dumped into his/her lap. The grand finale almost makes up for it though.
Porting Disaster: In the Playstation 2 version, the quality of the voice clips is wildly inconsistent throughout the game. Most of the time, they sound fine. But sometimes they sound like they're being played back through a telephone. This is sad, because in most other respects, this version is actually superior to the PC original (better graphics, a control scheme that's better suited for the PS2 controller, etc.).
Scrappy Mechanic: Monkey Kombat might have been tolerable if not for the fact that the game forces you to write down both the stance switching commands (of which there are about twelve) and which stand beats which, since both are randomized on each playthrough and the game provides no reference for them. On top of that, it can be a chore to learn the switching commands early on, as your opponents have a nasty habit of immediately switching into whatever stance beats the one you start off with and just staying like that for the rest of the fight, meaning that you'll be on the losing side of many Curb Stomp Battles until you've learned enough commands to actually get anywhere.
The general consensus among Monkey Island fans is that this one isn't quite as good as the previous games, not only thanks to a weaker script, but also thanks to control issues inherited from the Grim Fandango game engine: The game uses awkward tank-style controls for movement (in the style of Resident Evil) instead of the previous games' point-and-click interface, and using inventory items and interacting with the environment requires the player to shuffle one-by-one through a list of available options.
Unintentional Period Piece: Another major problem with the game. So many of its jokes are based on Turn of the Millennium pop culture that, today, they fall horribly flat. The plot, meanwhile, spoofs a lot of social issues that are far less relevant now than they were in 2000 (such as big corporations dehumanizing middle America). It's like American Beauty: The Game.