While ToB and Diablo does share a similar combat focus, the actual gameplay is still very different (real-time-with-pause tactical/party combat vs hack'n slash clickety-click).
Harder to believe that I bought this shortly after it came out and let it sit on the shelf for close to a year before playing it! To be fair though, I was finishing grad school at the time and barely had time to sleep. I got canned from my job in May of '01 and the first thing I did was try to load this puppy up....only to find out one of the discs that came with it was bad. Thankfully Best Buy let me exchange it without a receipt.