If he is one of the "greats" of his generation, then his generation must have been a really underwhelming bunch of cricketers.
Make no mistake, I like Clarke as a batsman but in this era, 8000 runs @ 49 odd is good, not "great". Why I say a few good years? Check his career stats. He averaged above 50 in test cricket in only 5 calendar years of his career (which spanned 12 years). And he was largely just a home track bully. His home average of 62 stands in stark contrast to his away from home average of just 39.5. He made good runs on flat Aussie wickets against some substandard bowling attacks, and while he toured he was mediocre to good, as demonstrated by his career stats. His highest 'away from home' (barring NZ) average is a mere 42.8 (in SL).
His ODI numbers are too not that great, although his fans would like to tom-tom his career average of over 45. Which is largely negated by a substandard strike rate of 78 (ie a run rate of 4.7 per over) in this era and inflated by a plethora of not outs (a fifth of all his ODI innings).
One area where he stepped out really was as a tactician. I admire him a lot for that, although his tactics were largely foolhardy outside Australia - the best (or worst) of them being a first day declaration at 239 and ended up having egg on his face seeing his team getting decimated by an innings and a ton of runs.
So yeah, Clarke is no way in the league of 'greats'.
Since you wanted a post critique:
AB De Villiers, arguably the best Test batsman in the world throughout the past 5-10 years, has 8000 runs at 50. He has averaged over 50 in six of his twelve years of test cricket.
Hashim Amla, who is also undoubtedly a great of his generation, has averaged 51 for his 7.4k runs. He also averaged 50+ in six of his twelve years of test cricket.
Yes, Clarke averages 62 at home. I wouldn't place him above either of the batsmen mentioned above him, but there are very few batsmen of his generation besides them that could be argued to have had a better career than him (presuming you don't try to lump him into the Tendulkar/Kallis/Ponting/Lara/Sanga/Dravid generation, which was potentially the most stacked generation of batsmen in Test cricket history). It's worth clarifying at this point that TheJediBrah claimed him to be 'one of the greats
of his generation.' If you see him as most do - as sharing a 'generation' with AB and Hashim rather than scrambling to shift him into the Lara/Tendulkar/Ponting era, he pretty clearly is a top 5 Test batsman of his generation, which is a synonym for 'great of his generation.'
Regarding ODIs, I think most would agree that his average of 45 isn't the be-all and end-all. SRT averaged similarly but you will never find someone saying they were at the same ODI level.
That said, a SR of 78 isn't the worst. Jacques Kallis struck at 73, Angelo Matthews strikes at 85, Graeme Smith struck at 80. JP goes at 84, while Mohammed Hafeez goes at 75. All in all, 78 is on the slow side, but certainly not unforgivable.
He was a good ODI player. Not nearly as good as your Tendulkars and De Villiers, but good nonetheless. His ODI numbers actually are good. His role was never to be a big hitter - Aus have routinely had enough of those already. He performed his role very well in ODIs.