I've heard him do a decent M2 with St. Louis in the 1990's that was marred by that weird "Rattle-ism" in the opening measures. (One thing that was excellent about that concert was what the Mahler was paired with: Ravel's song, Kaddish. It was a nice choice.) His Telarc M2 was much better.
He did what I thought at the time was an excellent M3, with Nancy Maultsby as soloist. I kinda wish I could hear that one again, to judge how good it really was.
The M5 I attended made it's way into "The Slatkin Years" boxed set, which he felt was one of his best performances with the Saint Louis Symphony. (It's my understanding from a source that the orchestra didn't feel it was all that great.) I picked up an extra set at a recent book fair, and if someone would like it, shoot me an offer for a trade, and we'll talk. I like the performance, and I don't mean it as a slam, but I really wish he would've picked the M9 he did from a few years earlier.
I was also present for his M10 (Mazzetti) concerts. The RCA recording was billed as "live" going into the concerts, but there were so many distractions during the nights I attended, (sirens from emergency vehicles screaming down the street, coughs, etc.) that the quietness of disc leads me to believe they chucked that idea. The RCA performance also a much lower voltage than what I remember in concert.
Lastly, he did a fine M7 as conductor laureate. It was better than Welser-Most's performance when he was here on a guest gig.
Coda: looking back, I also recalled attending a M1 with him from late in his tenure. I can't recall NOT liking it, but it must not have made a huge impression. Yo-Yo Ma did a work by Richard Danielpour on the first half that I do remember liking well enough. (I keep my ticket stubs, and routinely forward the newspaper reviews from a library database for posterity.) I happen to like Slatkin's Telarc M1 as much as his M2. If it were to come out on SACD, like the M2 did, I'd grab it. It's phenomenal on vinyl, too.