Not just glitches? What else? It's literally just glitches.
There were no new additions? Besides the new detective mode? More enemy types that made combat a whole lot more varied? Fast Travel Batwing?
The problem isn't glitches. Lots of games have glitches, but the problem is the severity of the glitches. I had to go through I Am The Night Mode twice because, halfway through, at the Royal Hotel, the game glitched and I lost all of my gadgets except those that I started out with. Meaning my remote claw was gone, meaning that I couldn't use it to ascend through the parking garage, or that, as I am fighting Bane, at the very end, on my second run through because I had to restart I Am the Night mode during that last bit of ****ery, my gadgets once again disappear. Thankfully, the QTE where he rushes you at the very end was scripted, and so, I didn't need the Remote Claw that I was freaking out about, but the point still stands; a "glitch" is Batman's cape clipping as he walks around in Arkham Asylum or how a thug might slip through the invisible wall and fall off a rooftop after you hit him.
What these were, though, is game breaking, and when WB Montreal came out and announced that they weren't going to bother patching them, in favor of devoting their resources to the production of more DLC (which, as far as I'm concerned, is content that should already be on the disc, and that goes for everybody, not just WBM, but I still buy into it because I'm a sap), that's when they undid any goodwill I had towards them. Truthfully, you're right. The glitches were my only problem with the game, and that's why it pissed me off so damned badly when they went in that direction, because I felt that they weren't doing a great product the justice it deserved. They succeeded! They made an "unofficial" sequel that, for all intents and purposes, wasn't a generic cash grab, but, then, they treated it like it was, and, in my estimation, ruined the game. It disappointed me that much. I would much rather that it sucked and that I didn't like it because then I could've written it off, but, by the end of it, I was just disappointed, and a little sad, that they didn't have enough faith in their work to try to improve on, literally, the only thing that needed improvement.