> I'm on deployment, so no downloading and playing with stuff for myself. Did a search
> for retroarch and the first page of results didn't exactly cover my question...
> How does retroarch do in comparison to MAME with regards to all the stuff that was
> merged from MESS? Not in terms of accuracy, but playability?
> Can I use the very same files from the most recent MAME and play them with retroarch?
> What does Retroarch do that MAME does not, and vice versa?
Retroarch isn't an emulator, it's a frontend, although most people seem to think it's an emulator because it gets bundled with all the cores.
Think of Retroarch as some ultra-dumbed down console like experience, no real flexibility, everything has to fit a 'console-like' model, lowest common denominator stuff, advanced functionality is lost, black box, nobody cares about how bad any of the code is as long as it 'works'.
The cores are just hacked up, recompiled versions of old emulators so often considered 'more mature' than the MAME ones, because they do a 'better' job, but at the same time it's very much anti-development, the cores don't work together, it's just existing emulators glued into one place with no sharing of core code, no mutual benefits, no reason to try and write PROPER code that works across multiple systems, but instead basically relying on incomplete 'good enough' per-game/system implementations of things. Compare it with MAME where the individual CPU cores and device cores are tested and refined by their use across many, many systems, with every system acting as a verification that a change is good.
It's a bad thing for development in that sense, because people will use it and claim it's better and kill any drive people have to try and write better emulation code for the various components. It can be very demotivating for people who are trying to do things right if everybody keeps claiming the people who aren't doing anything are doing it better. For future generations it's important to nail down the emulation of each component so you have a M68000 core that accurately emulates the M68000 and can be reused anywhere, not 5 different M68000 incompatible M68000 cores written to different that emulate only a subset of features needed by one specific piece of hardware so can't easily be reused. MAME has spent a lot of time moving away from the 'per game implementation' model, instead unifying components and improving things along the way for the benefit of everybody, the RA line of thinking pulls things back in the other direction, it's a regressive way of thinking.
Personally I consider it a parasitic cancer for this reason, I know that's maybe not the most popular opinion, but it presents a false impression of being something better without actually doing anything at all to encourage emulation development, more encouraging people to hang onto older emulation cores. Unfortunately, as people are generally selfish and can't see outside of their own bubble of 'want to play free games' it continues to gain popularity despite all this. Convincing people that developing a proper well-tested unified code-base is a much more important cause is practically impossible because they simply don't care.
RA contributes nothing at all to actual emulation, just keep that in mind, especially if considering donations or the like.