As great a player as he is, I'd like to see him challenged more on a weekly/seasonly basis. The fact is that the difference in quality between the team he's playing in and the 19 other club's in their division is chasmic. It's giving him a constant platform to show all his talent with little adversity to overcome. Of course, he'll be chuffed with that service and freedom to express himself and who can blame him but the best way to judge a player's influence and overall level IMO is when he's playing in difficult circumstances or in an ultra-competitive environment(see Maradona leading Napoli to Serie A in a league containing teams like Sacchi's Milan, Juventus, Inter with Bergomi, Matthaus, Klinsmann, Udinese with Zico, Roma, Sampdoria with Vialli and Mancini, Lazio etc). Until Messi is put in that kind of position with either Barca declining or La Liga spreading it's talent further than 2 club's, I'd hold back on all the platitudes of him being an all-time great like Maradona, Cryuff, Pele and co.
He's the best player of his generation by a mile, whether that generation is as demanding of top player's of the past or as competitive as La Liga in the 70's, Serie A in the 80's and 90's is open to debate IMO. We'll only truly know how great he is if/when Barca's standards slip, let's be honest, he's hardly set the world alight with his inferior national team and was nowhere near as prominent during the transitional phase Barca went through during the latter months of Rijkaard's reign, although overcoming his injury problems and maturing as a player has no doubt played a part in his current excellence aswell.