On driving entertainment value alone, it's a tough transition from a 6MT E90. The modern tech and features, and yeah, creature comforts would have to offset the loss of pure driving factor.
Bias alert: I think the E90 M3 is the best all-around car ever made. If I could snap my fingers and have a track ready, mechanically sound (rod bearings, etc.) E90 instead of the AMG, I'd do it no hesitation. But as indicated, was time for the wife to win one and I only have so many garage spaces.
Are you entertained by tech? It has plenty. Two big screens, both of which can be pretty intuitively controlled on the updated wheel. (You basically don't have to visit the center console controls.) Bluetooth music, apple carplay, Burmeister system all excellent. Full spectrum ambient lighting options, multiple instrument cluster design themes, numerous settings for the info displayed inside of the speedo and tach… head up display (also customizable), etc. etc. etc. It's jumping to an iphone 11 from flip phone coming from an E90.
The drive mode dial in the lower right, and customizable buttons lower left that can be set to toggle exhaust, dampers, trans, and more, are great. The wheel itself is good, but too hard imo. nobody does steering wheels as well as M.
Lane assist + distance control = autopilot. Not as good as Tesla's, but still very usable on well-marked roads.
Despite the relaxed vibe overall, the current gen C63 S AMG is probably more track ready in my experience than a stock E90 or F8X. I don't know if mine will ever see the track, but I hammered on my buddy's '17 pretty hard and enjoyed it. Brakes, cooling, everything was solid. It's just lacking tires for advanced pace – 245 front, 265 rear stock. (Rear is narrower than incoming G8X front.)
Updated 9 stage traction control would be an advantage for track newcomers or casuals vs. M's of any gen up to G8X.
Performance seats are better than anything M pre-G8X in terms of track/performance driving support + day to day use + looks. I have the heated & cooled.
Transmission – there's no getting around, it's just alright. To add to, I don't like the thick paddles or clunky paddle action, but still use them from time to time. I'm probably in comfort setting and auto 90% of the time. That's just what suits the character of the car. It doesn't constantly goad you into bad behavior like an M car. Or, maybe I'm just getting old.
In auto, it is responsive. Dial up the modes toward sport plus and race and it stays ready to rip. It is not sloppy, that's not how I'd describe it. It's a big step forward from the old Merc slushbox, just not M dct.
Engine – in the context of modern options, it's fantastic. Anyone who says otherwise is full of it. Loud, responsive, powerful, and always present. Cruising at 50 mph and between 1-2k rpms in 9th gear, it's still rumbling away. And as pointed out above, rumor is a 4 cylinder for the next gen 63. I'm a sucker for "end of the line" types of vehicles and features.
Hope this helps. It would be a major departure from the E90, but if you're ready for a transition vs. a replacement that would be close in character, then it could be a match.