Hip hop has changed since Shady's been away; not the music - those weeks-long cycles where styles were chewed up, spat out and replaced had been long-gone by the time he arrived in our lives - but the way the music reaches people, and the impact it seems to have.

Encore wasn't the first album to get hijacked somewhere between the studio and the shops and find itself sprayed all over the net before it dropped, but it was one of the biggest early victims of widespread online piracy and among the last of the true "event" releases in hip hop history. Today, everyone's heard an album weeks before it's on sale, the audience doesn't seem to feel that classics happen any more, and artists are caught between listening to the chatter on the fan forums and switching styles to satisfy the fickle marketplace, or going their own way and doing their best to ignore the hoopla and paranoia.

It's a tricky place to return to, then, after five years away, two or three of which - so the stories go - have seen Em holed up in Howard Hughes-like seclusion. In one sense, that ought to have helped: if one of hip hop's unarguable colossi has shut himself off from the world to the point where what anyone else is doing, saying or thinking can't reach him, he might have been moved to make music that is undeniably his own. Eminem's career has been one defined almost exclusively in terms of reference to others; whether he's talking about Kim, or Hailie, or analysing his place in pop culture, or self-consciously railing against critics who want to circumscribe his subject matter, he's always seeing himself through the eyes of others. As a result, he's yet to make the record anyone who's ever properly listened to him knows he is capable of.

OK, so Relapse isn't here yet and we're confining our observations to one track - a track on which he gives two thirds of the mic time to his illustrious associates (both - or so we're repeatedly assured - with albums to promote, of course). But if this is a guide to what to expect, then that classic Em album may still be some way off. At least Interscope have managed to turn what looked like an embarrassingly low-key return into An Event - belatedly backstopping the January leak with an iTunes release has seen high global chart places and first-week sales of near half a million in the US alone - a record high for a week one download. Yet as a song, and as the vehicle by which it reintroduces hip hop's reclusive genius to a world that can't be anything but receptive, it's depressingly anti-climactic.

There's nothing much wrong with Dre's beat - indeed, for the first few seconds of the first time you hear it, the blend of sleazy horns and Billy Joel-via-Kool G Rap piano rattle sound genuinely thrilling. And there are some neat touches in the song, from Em's clever, knowing riff on the superstar trio's absence from the game ("the elephants have entered the room") to the way 50 starts to sing his verse, keeps going just long enough to make you think 'No: there's no way he's keeping his competition with Kanye going to the extent of abandoning rapping too...', before he gets down to the gravely voiced rasp that couldn't be anyone else, and you realise you've been had by a consummate gamer.

But there's little else to really grab hold of and hang on to here, in a formulaic song with a tired chorus and - yet again - an almost total lack of anything interesting to say to make up for the slick but mechanically, reflexively commercial chants of the chorus. (A chorus and title which has the greyer-haired among us pulling out our YBTs albums and dusting off the long-forgotten Tap the Bottle, and noting that the comparison isn't one that seems particularly to favour the newer song.) It's just another Eminem track, solid yet unspectacular, and its reception proves how much he's wanted and needed without the record ever really managing to show us why.