I'm no expert on this subject, but I have looked into Med/Psych programs quite a bit. I've talked with the program director here at UIowa and got a lot of good information.
I would
not say that these programs are glorified Psych residencies. They offer thorough training in both fields and prepare one fully for boards in both, as well. Just as in any other residency program, each Med/Psych program has its pros and cons. These can range from location (and therefore patient population); doing 6 months Med to start, then 12 Psych, and alternating like so; doing 6 months alternating of each; electives offered; and emphasis placed on the integration of both fields (e.g., some schools may have a dedicated Med/Psych unit). For specifics, check the AMA's FREIDA website for program homepages. Here's a
link to UIowa's Med/Psych program website.
One nice thing about the field is that it's not all that competitive. Whereas, the IM categorical at say, Dartmouth, may be much harder to get into rather than the Med/Psych program. I'm really not sure if that's true, but it's quite possible.