I've been working with AIX since 1990. Prior to that a bit of SunOS. AIX is is different but generally well thought out. Most people who hate it simply aren't used to the differences. Lots of feature that we take for granted in today's Linux existed in AIX 25 years ago.
Tivoli Storage Manager is a dream. I remember setting up a high-availability TSM (well, ADSM at the time) server and having a client backup running during fail over testing. Client connection failed, continued retrying until the server was back up on the other node, then the backup continued where is left off. Transaction backup with rollback and resumption after server fail over! Try that with NetBackup or Networker or Avamar or CommVault.