I can't say I was disappointed, because I liked it at first, but Gloomhaven really became a drag after a year or so of playing. I feel like you really need to be invested in the lore and story to get anything out of it after a while, otherwise it's basically glorified, over-complicated chess. It doesn't help that 90% of scenarios have the same winning condition: "kill all monsters". I feel like there could have been a lot more depth to the actual gameplay, and not just the fluff in-between. What's more, each scenario takes 2-3 hours at best, and to make any real progress you need to set aside at least 6 hours per session, which is crazy. It's basically a job at that point.
Also, in the later stages, when you have a level 3-4 party with unlocked classes, encounters become exhausting, because you need to keep track of a million modifiers and buffs/debuffs, sometimes cancelling out eachother twice. And it's not a Gloomhaven session if you don't keep going back to the BGG forums for rule clarifications. It's a mess of a game, really.
After seeing what the scenarios with different win conditions looked like I am GLAD most were just "kill all monsters".
As for session length we always played just a single scenario (unless we lost the first super quick). It took us a good year maybe one and a half to play through the campaign. IMO the problem is less the session length and just how much of a time hog this game is in general. We're talking 150+ hours dedicated to a single game.
Yeah, I see your point. My group could only meet up once every so often due to differing work schedules and adulthood responsibilities, which I guess contributed heavily to the slow progress and the fact that we wanted to cram as much progress as possible into a single session. We were going on 2 years when I dropped out, and had made it halfway or two thirds into the campaign. The sad thing is that we could've exhausted several other games by that time instead of barely finishing the one.
Despite my rant, I'm not trying to put people off Gloomhaven entirely. It might be the best thing ever for some people. Just know what to expect when getting into it.
I can't blame you. It literally took us pretty much weekly sessions for over a year to reach the final scenario. That's a daunting comittment. I actually low key burned out on the game a few times during that period. But it always pulled me back in again.