It's sad actually, because in Gloomhaven there's some very good gameplay, the classes play very differently and during the course of the campaign when mercs retire (after reaching their personnal goals) you can hire completely new classes to add a lot of variety to the card building.
But the scenario design that does not allow you to do anything other than the absolutely optimal card play (at least if you want to win those, very long to play, scenarios) is really frankly horrible to me as it transforms too much what could be a very good strategy/tactical game with card building into "only" a puzzle game in which there's only 1 solution to find.
Basically Gloomhaven is designed for those that really like the "find the correct combination and order to play cards to win" type of game as so far from all the scenario i played and managed to win, everything else is doomed to fail.
I really wonder how the boardgame can play with more than 1 player, i mean you need to coordinate mostly exactly your mercs positionning (the scoundrel class has many cards that actually depend of your ally or enemy position to do their best results) and when to play their own cards and in which order if you want to complete objectives before exhausting your mercs decks, something that is doable if you're managing all the mercs on the board, but with multiple people with each their own ideas on what card they want to play and where they want to move their mercenary... that must be hell if you hope to win each scenario
But in the actual boardgame , like in any boardgame, you can come up with your own modified rules to take care of the design shortcomings and unfun parts, something you can't do in the videogame sadly.
At least a good point of failing is that Gloomhaven does not remove the gained XP and Gold looted, and also does not remove whatever you found in a chest, so even failing your mercenaries will still gain more power (and the enemies will too as their health is based on your "party level" )
Now if only the AI decision code and scripts were faster, scenarios already take a long time by default and those extremely slow to do anything AI really increase the scenario length a lot uselessly, making replaying them more of a pain than something fun.