Hi! I registered an account to post in this thread. I'm a pretty big fan of GBI, so I figured I'd post my feedback. I'm sure any issues I might have are known by the users here and Extrems already, but here's my setup and experience:
I'm running GBI via Swiss with the SD Media Launcher on my PAL gamecube, going to my LCD via a 'retro_gaming_cables' SCART cable to my Framemeister. I'm using the Raphnet SNES to Gamecube controller adapter, which is currently being discussed above. The control layout isn't perfect but it works well enough for my needs.
Currently, the biggest issue I have with GBI is with horizontal banding, or screen tearing (whichever descriptor works better here). I believe this was brought up earlier in this thread, but basically it involves constantly shifting pixels on specific lines, maybe in every third of the screen or so. This is exacerbated by certain parts of games that move a lot, like the ice shield card in Circle of the Moon, which causes the screen to 'wobble' in this way on whichever lines the ice inhabits. This issue is present in all versions of GBI (regular and both low latency versions). This also occurs sometimes when using the swiss menu or just booting up the media launcher interface, but is much less pronounced, and doesn't affect regular Gamecube games (of any region) or the Gameboy Player official disc.
Also, I've found with the LL and ULL versions that certain screens will cause either graphical glitches, or cause my framemeister to reset the resolution momentarily. Again, using Circle of the Moon as an example (I played a lot of this on GBI recently), the map screen via ULL is completely unusable as half of it gets cut off and moved offscreen. In LL and regular GBI, the map is intact but the lines look very squiggly, perhaps as a result of the above banding issue. With LL or ULL, saving the game in COTM will cause the aforementioned resolution reset with the framemeister, without fail. I've had this occasionally happen during regular gameplay of other (non GC) games with the framemeister, but never had it trigger so consistently. This may be an issue with my FM's firmware, though. None of these issues are present when using the standard Gameboy Player disc (which is still run through swiss, as my disc is Japanese.)
With all this said, however, GBI is still a much preferred option to the GBP disc. The lack of that gross border makes the games look so much nicer and easier to upscale; the accurate colours pop so much better in RGB; and the latency makes the games actually playable compared to the GBP disc. I played several hours of Castlevania via the GBP disc and thought it was the game's fault that the combat was so clunky but after switching to GBI (ULL) I found it much more fluid. You are doing a bang up job on making the best GB-on-TV experience and I've been very happy to follow the development of this software since it was first released. Thanks and sorry if you're sick of reading about these same issues that you already know about!
Edit: I just tried out the new version and I'm super stoked to see the ability to edit arguments with the regular GBI dol! Wow! I had a whole thing in here about not being able to do that but I removed it straight away, heh.