Sonic Pocket Adventure (Neo Geo Pocket)
This was the first handheld Sonic title since Game Gear and arrived on the back of Dreamcast's Sonic Adventure, while interest in the 'hog was rekindled after what was basically a no-show during the 32-bit era.

The Neo Geo Pocket was a great little machine, offering graphics of a quality somewhere between Master System and Mega Drive (or NES and SNES, depending). And this Sonic title combined the best of 16-bit Sonic 1 and 2 to create a very fun handheld Sonic.

Above: What's not to like? It's Sonic 2 just... different. And chunkier

The bonus stages of Sonic 2 made a welcome return, now with improved scaling. The regular zones were simplified versions of Sonic 2's for the most part, with Aquatic Ruin, Chemical Plant and Casino Night all looking pretty close to their bigger siblings, albeit without the multi-layered backgrounds.

If you can find a copy on eBay and love Sonic enough to buy an obsolete console just to play this, it is worth picking up. But be warned: it is quite basic compared to modern handheld offerings or full-fat 2D Sonic, so we can't really give it an 'essential' recommendation. It's better than Sonic Chaos, though.