June was Sonic's 20th anniversary, and later this year Sega celebrates with Sonic Generations, a project that aims to combine the hedgehog's best and, admittedly, worst moments. 3DS owners get a very different version to PS3 and 360 fans, both for better and worse.

Sonic Generations on 3DS joins traditional 16-bit style platforming with more modern Sonic Colours gameplay, with a level from both styles on offer for us to play. The 16-bit Green Hill Zone looks pretty, though less visually packed than its HD console brethren, but in this version the frame rate leaves a lot to be desired: at its best the game managed 30 frames per second, but this noticeably dropped when Sonic took damage or entered crowded areas. Turning the 3D effect off helped the frame rate, but on the whole this is not quite the smooth visual presentation you'd expect.

The game doesn't handle quite as you want either. Fans jumped on Sonic the Hedgehog 4: Episode I for its unfaithful physics, and in its current incarnation Sonic Generations is similarly messy: often Sonic jumped too far or came to a stop too quickly, and overall the running felt slippery.

Surprisingly the Modern Sonic stages played better, with level design that'll be familiar to anyone who's picked up a portable Sonic game since 2006: lots of boost pads and grind rails, with an impressive-looking set piece where a giant totem pole threatens to flatten the heroic hedgehog. Those who can't get along with the DS Sonic games' boost system will find little to enjoy here, but it at least feels faithful to its source material, hardly surprising considering it's developed by frequent handheld Sonic overseers Dimps.

The third and final level on offer was against the Big Arm boss from Sonic the Hedgehog 3's Launch Base Zone, played through as Classic Sonic. The attack patterns are slightly different, and the stage and boss certainly look good in 3D, but it played slower than we remember and posed little challenge, though of course this is just a short demonstration.

We're big Sonic fans here and have high expectations for Sonic's big 20th anniversary game: if SEGA is to acknowledge the hedgehog's history, it has to replicate or improve on the classic mechanics, but there's much work to be done here. Sonic feels less in your control in the 16-bit style levels than the boost-heavy, homing attack-packed Modern Sonic stages, which is not something we expected to say. Add in the choppy frame rate and slippery physics and we must admit our first impressions are not favourable. With only a few months until launch SEGA has a lot of ground to cover to bring the hedgehog up to speed.