Far too many things went wrong, but a few went right:
What Went Wrong:
The Roster:
If you're going to tout that a game includes All-Stars, you have to secure the rights to at the very least Crash and Spyro. Negotiating a deal with Activision is no easy task, but that needed to be done before developing the game.
There were also attainable first party characters who were inexplicably absent. A Chimera would have been a terrific representative from Resistance, and would have had an easy to create play style and super abilities thanks to the unique weapons in the franchise.
In the end, all of those exclusions meant that a bunch of b-tier stars made the cut, many of which really had no link to PlayStation. Big Daddy is a cool character, but his franchise's first entry didn't even launch on the console.
The Super System:
In an attempt to establish a unique identity, different from Smash Bros, the super system was created. It seems like an okay idea on paper, but it didn't work all that well in game. There was no consistency between the each super, or the tiers of supers. Some characters had easy to land level 1 supers, others didn't. Some level 2 supers could easily get a few kills, some were still tough to get one. Some level 3 were automatic stage clearing cinematics, others relied on player control to hopefully kill all the other players.
This could have all been balanced a bit had a hybridized model been considered where players had health like in Smash. Supers could have been encouraged to take massive amounts of health, but missing one wouldn't have had such a detrimental effect.
The UI:
It was just bad. Granted, had the game been better, I'd have dismissed it. Many people complain about some of the Smash UIs. It was just another indication that little effort was put into the game as a whole.
What Went Right:
Releasing DLC Characters:
Sure the characters weren't the greatest choices, but the execution was an interesting idea. As a huge fan of Sony's first party, I thought it was a cool idea to include DLC in other first party releases. Hades and Isaac Clarke were included for free with God of War Ascension. There were a lot of possibilities here. Had the game been more successful and that trend continued, we could have got Joel and Ellie with TLoU, Bentley and Murray with Sly Cooper: Thieves in Time, Kutaro with Puppeteer, Iota and Atoi with Tearaway, or jumped into the indie realm and partnered with Drinkbox for Guacamelee!'s Juan Aguacate or FuturLab for Velocity's Kai Tana. Had a Resistance 4 ever come around - I'm still sad - that would have been the prime time for a Chimera.
Alt Costumes:
Some of the alt costumes, many in the pre-order bonus were fantastic. They forwent the easy color swap for an entirely new character model. Swapping Kratos for his brother Deimos, Cole becoming Kessler, and reducing the Big Daddy to the plush doll version of Big Daddy were brilliant, and great fan service. Sweet Tooth's Outcast skin, which was pulled from his inclusion in Starhawk was another solid idea.
For as much as PSASBR bungled, I'd still like to see Sony try again, providing they listen to a lot of the feedback and incorporate some of the Smash DNA. They've got the IP to sustain a game. And with a few new characters like Knack, Delsin, Fetch, Bloodborne's Hunter, and Aloy, plenty they never used, and many more on the way, they could easily experiment again with the DLC.