For a comparison, Thief: Deadly Shadows also suffered from having to cram its levels in the xBox's limited RAM, but its gameplay kept a better semblance of its precursors' and it's remembered more fondly than IW.
I had the complete opposite opinion of Deadly Shadows for ages ever since I first played it and Invisible War for the first time. It took Thi4f being as bad as it was for me to finally find some good in Deadly Shadows, before that I absolutely hated the game because it felt like a clunky piece of garbage with half of the movement options stripped out of it from the previous games. Deadly Shadows looks pretty, the lighting is nice and the way it wraps up the trilogy storywise isn't absolutely woeful, but it is not a good game, and the gameplay is not good compared to 1 or 2 by any stretch of the imagination. I'm of the firm belief that Deadly Shadows apologism stems from people who played it on Xbox as their first ever game that wasn't as straightforward as Halo or something, the same way everyone who now looks back on Fallout 3 fondly was 10 years old when they played it and thought it was super deep because it was babby's first RPG.
Anyway, back to the subject of Invisible War, when I first played it directly following Deadly Shadows and Deus Ex 1, I didn't hate it nearly as much as Deadly Shadows. It certainly isn't a good game, the character models are butt ugly, the animations and voice acting suck, the gameplay and writing is total ass compared to DX1 but it had the common decency to not control like an ARMA body simulator first/third person QWOP game like Deadly Shadows did. And for that I am thankful to Invisible War, for not being designed around being a third person game for console babies that put half the dev resources into making it control like a third person game even while in first person mode. Climbing gloves suck ass compared to rope arrows, the removal of forward leaning and reliance on third person is AIDS and Garrett instantly dies if he submerges in waist high water for some fucking reason - the levels are built to match, like the "Sunken Citadel" inhabited by a race of subterranean fish people only having puddles of water for you to trot through.
And yes, a fan patch may stitch some maps together here and there, but it doesn't address the underlying issue that the maps are almost entirely devoid of verticality and complexity compared to the previous games thanks to it being a RAM-cucked Xbox stillbirth on a fucked up mutant version of the unreal engine. The loading screens in vanilla are dogshit, just like in Invisible War, but they're not the biggest problem with the game by a long shot. The Sneaky Upgrade also does pretty much
nothing to address how clunky and disgusting the movement is in Deadly Shadows, if I'm remembering right, probably because the movement of the game was designed
wrong from the ground up. Alex Denton moves like an olympian in comparison to Xbox Garrett.
TL;DR Gameplay-wise, Deadly Shadows is an equal to Invisible War. Standing proud shoulder to shoulder with their 64MB of RAM to spend on their retarded level design and also I have a deep seething nerd hatred for Deadly Shadows' movement.