Each team is VERY different, as one co-worker put it, IBM is essentially a massive company full of mini-startups (a.k.a individual departments or teams). My team had excellent mentorship/support, the team was very approachable and knowledgeable and were always willing to explain concepts to you.
The work itself was somewhat interesting, but felt like IBM was trying to "catch up" to the data science hype. This is expected for a large company though. Similarly, the work hours are very flexible but some people work insanely long hours due to the large amount of work that can get handed to you.
Finally, one of the biggest negatives to IBM is the workplace politics. There are so many different levels of management that information can get diluted down the management chain which may also lead to unrealistic expectations. My direct manager(s) did their best to shield us from that, but things occasionally leak through.