Sonic 1 is a good game but the sequels are better. You don't put it on a Genesis comp unless all four Sonic titles are included (though I do expect that in the final lineup).
Sonic 1 is by far the best selling Genesis game. It's the equivalent to Super Mario Bros 1, where it was the killer app that made everyone notice the system in the first place and most people who bought to system either owned or played it. Even if most fans prefer the sequels, Sonic 1 is still the most iconic game in the series to the overall general public.
Of course speaking of the Sonic games, I wonder if Sega will be able to work out deal to get Sonic 3&Knuckles in this as well. The last time S3&K was released was an early 2011 Steam port of the Xbox Live Arcade version from 2009 and hasn't been rereleased since. Many have speculated that because of Micheal Jackson's involvement with Sonic 3 there's some messed up issues going on with the copyrights which is why Sega hasn't released it since. I mean Sega released it a ton of times in the 2000's but that was before Michael Jackson died. Michael was well known for liking Sega games so I imagine while he was alive he had no problem with Sega still releasing the game but after he dead, his estate probably jacked up the price to an insane degree that Sega doesn't want to deal with.
I mean the recent Sega Genesis Classic Collection for Switch, PS4 and Xbox One has Sonic 1, Sonic 2, Spinball and 3D Blast but no Sonic 3 & Knuckles. That collection was less then a year ago and a huge omission which is why many speculate there's still a legal mess with that game. So I don't know if I would hold my breath for Sonic 3 & Knuckles appearing.
I had no idea that there were issues with Sonic 3 & Knuckles. That sucks because that is a mandatory inclusion and it being left off would be a big hole, particularly since it's a first party title and you normally would assume there would be no issues.
Sonic 1 is a huge game and I would say it should be included but the sequels should also be there. Sonic 2 at least for sure if Sonic 3 can't make it. Sonic 1 does compare to SMB1 but if the NES Classic had that but not SMB3 that would have been lame.
Is there any reason that Sega CD games can't also be included? If they could get Sonic CD on there then that could make up quite a bit for Sonic 3 being absent. And with Konami already on board imagine if they included Snatcher? I would buy this JUST for that.
We know Konami's involved so maybe Contra Hard Corps and Rocket Knight will make it. TMNT certainly isn't. Everything else revealed thus far is first party. It would be nice if they could get Capcom on board for Strider and Ghouls 'n' Ghosts. I think EA would be an obvious third party to get involved for the Genesis though I don't see stuff like Madden or NHL 94 being able to be included for obvious licensing reasons. But the Mutant League games, Road Rash, the Strike games, General Chaos - those should all be owned outright by EA. Another third party they should seek out is Thundersoft for Herzog Zwei and the Thunder Force games though I don't really know what company owns those rights.
For first party stuff I would expect to see the Streets of Rage, Shinobi, Golden Axe and Phantasy Star series. Maybe all of the Genesis games in the series. Hell the Genesis hardware is actually backwards compatible with the Sega Master System (the Power Base Converter is just a cartridge slot converter) so why couldn't they include a few SMS games like the original Shinobi or Phantasy Star? It isn't like they need to save those for a SMS mini.
If they could get the Mortal Kombat games on here that would be great but there are two issues. First of all that obviously moves this into an 'M' rating which they may not want and is largely unnecessary for a 16 bit system. Second of all, those games will control like crap on a three button controller.
If the emulation is good this can easily be a great system. Unlike Sony, Sega has a really strong first party lineup so it will take effort to flub the lineup even if they can't get much from third parties.