I've read more enjoyable ones. In terms of sheer enjoyment levels, Vulcan's Heart probably still comes out on top, but Vulcan's Heart has Spock/Saavik, pon farr, Romulans, Tasha Yar, and Sarek. I cannot be objective about that book because it is plugged directly into my id. The Entropy Effect is better written. This is hardly surprising given that McIntyre won a Hugo a few years before she penned it. Clearly the woman knows her craft. But I was frankly disappointed in Enterprise: The First Adventure and didn't know what to expect with The Entropy Effect. Having read it, I suspect that McIntyre may have phoned it in a bit with The First Adventure. Entropy Effect feels more polished, and more...weighty. In a good way.
Also, the cover art with a mustachioed, long-haired Sulu is a sight to see.
So now I'm reading Vulcan's Soul, which is a trilogy written by Josepha Sherman and Susan Shwartz, the same authors who wrote Vulcan's Heart. The Vulcan's Forge/Heart/Soul books is basically the canon of the Spock/Saavik fandom, which is a tiny little corner of fandom that I'm inordinately fond of despite not being especially active in it.
I'm meh on Vulcan's Forge, love Vulcan's Heart for the aforementioned reasons, and don't yet know how I feel about Vulcan's Soul. Based on the first little bit, I suspect I'm going to land closer to Forge than Heart, but we'll see.