Though not a 3500, I've got the 2500 CTD with the same drivetrain. So for it's been very reliable and I love the truck after 2 years and 30K miles. Fit and finish is outstanding IMO.
Yes, I did have the water pump replaced under recall and will soon have the trans interlock thing done. Every vehicle I've ever owned had multiple recalls so nothing unusual here. I've been on the forum for 14 years and everybody seems to love their Cummins powered Ram.
To me the reliability seems to be the same as the later Ford and Chevy trucks. I don't see one being more reliable than the other based on feedback from this forum, other than the flack from the old 6.0 PSD engine.
Nobody makes a bad truck any more! If you like the truck and it's in good shape, go for it!