A lot of things are indeed taken into account for rankings.
For a batsman, the factors are:
Runs scored
Ratings of the opposing bowling attack; the higher the combined ratings of the attack, the more value is given to the batsman’s innings (in proportion)
The level of run-scoring in the match, and the team’s innings total; an innings of 100 runs in a match where all teams scored 500 is worth less than 100 runs in a match where all teams were bowled out for 200. And if a team scores 500 in the first innings and 200 in the second innings, a century in the second innings will get more credit than in the first innings (because the general level of run scoring was higher in the first innings)
Out or not out (a not out innings receives a bonus)
The result. Batsmen who score highly in victories receive a bonus. That bonus will be higher for highly rated opposition teams (i.e. win bonus against the current Australia team is higher than the bonus against Bangladesh.)
For a bowler, the factors are:
Wickets taken and runs conceded
Ratings of the batsmen dismissed (at present, the wicket of Kumar Sangakkara is worth more than that of Makhaya Ntini – but if Ntini's rating improves, the value of his wicket will increase accordingly)
The level of run-scoring in the match; bowling figures of 3-50 in a high-scoring match will boost a bowler’s rating more than the same figures in a low-scoring match
Heavy workload; bowlers who bowl a large number of overs in the match get some credit, even if they take no wickets;
The result. Bowlers who take a lot of wickets in a victory receive a bonus. That bonus will be higher for highly rated opposition teams
Bowlers who do not bowl in a high-scoring innings are penalized.
The players’ ratings are calculated by combining their weighted performance in the latest match with their previous rating. This new ‘weighted average’ is then converted into points. Recent performances have more impact on a player’s rating than those earlier in his career, but all his performances are taken into account. A great player who has had a lean run of form will still have a respectable rating.
Players who miss a Test match for their country, for whatever reason, lose one per cent of their points.
http://www.icc-cricket.com/player-rankings/about
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ICC rankings are not as lulloo as we think they are.
May not be perfect but they take a LOT into account when it comes to player rankings.