About Regen
Regen is a Sega Genesis/MegaDrive emulator written for maximum accuracy.
The compatibility is probably at or near 100% for licensed games.
About the accuracy, well, Regen already runs many games even more accurately than Kega Fusion 
Everything has been accurately emulated to the last detail.
If you find a non-working game (licensed) please report it immediately. You can either send an e-mail, or post about it here.
Here is a rough list of things present and missing in Regen:
Present:
——–
* Main 68000 CPU emulation using Musashi, specially modified for Genesis emulation
* Sound CPU, Z-80, emulation using RAZE
* VDP:
- Scroll planes A and B with vertical scrolling
- Window plane
- Sprites
- All sprite limitations
- Sprite masking
- Shadow/Highlight
- Interlace mode
- DMA transfer (all modes)
- Accurate H/V timings
- Accurate DMA timings
- NTSC and PAL emulation
- Sprite collision and sprite overflow flags
- FIFO and VDP write timings
* Highly accurate YM2612 emulation, with special High Quality mode
* Very accurate PSG emulation
* Stereo sound output
* IO ports emulation
* Support for 6-button pads, Teamplayer, 4-way play, Menacer lightgun, J-Cart, Mouse
* Special SVP chip (DSP) supported. Needed by Virtua Racing.
* Serial EEPROM emulation
* Emulation of special on-cartridge protection chips of unlicensed games
* Save/Load states in Genecyst format (used by Kega and Gens)
* GameGenie/Hex/Pro Action Replay code support through cheat files
* Full backup ram support
* Kega Fusion plugin support
* Zip an 7zip support
* Nice 68000 debugger
* Many many other things
Missing:
——–
* Plugins that scale the output by 2 are only supported
* No Sega CD support
* No 32X support
* No Sega Game Gear/Sega Master System support