I might buy Sonic 4 though.
Save your money, man. Sonic 4 episode 1 and 2 aren't bad, but their... really bland. Their alright the first time, but their titles you won't go back to, not with all the other options you have. If they were 5 bucks a piece, maybe... But 25 dollars all together? For that money, you could just get Sonic Generations. I know you said you don't want to give the 3D games any more chances, but this is defently worth giving a shot.The remade 2.5 Genesis levels are a blast to play through, with remixed music and the choice to swap the levels soundtrack with other tracks. The 3D sections with modern Sonic are like those in Sonic colors, maybe a little tighter and easier to get the hang of, but there's something grand about tearing through Chemical Plant Zone at high speed in third person.
If you want a major throwback to the old days, then check out Generations. Even if you don't like the 3D sections, the classic Sonic segments blow anything Sonic 4 has out of the water- and come complete with missions and alternate level layouts.
Or if you haven't tried it, check out the revamped Sonic CD that came out a while back on Steam, PS3 and 360. At 5 dollars, it's a steal.