All the books or tv series I have seen about the American Civil War depict McClellan as a poor and indecisive leader. Is this assessment fair or is it an overstatement? What do military historians generally think of him? Thanks
I answered a similar question a few years ago that addressed why McClellan's men were so loyal to him, which dipped into an analysis of his command and generalship. You can find that here: https://www.reddit.com/r/AskHistorians/comments/3e2vmb/why_were_george_mcclellans_men_so_loyal/ctb1o34/
Happy to answer any follow-ups though.
In addition to petite-acorn I have found answers by /u/dandan_noodles (who also wrote an original answer) and /u/QuickSpore and /u/67thtigers in Why was General McClellan so widely considered to be incompetent?