Hucards you shouldn't have any problems with. If your going to run across any problems it's going to be with the cds and the cd systems. I've rarely ever heard of people having problems with playing hucards.
Generally Hucard graphics are as good as a Genesis and sometimes better. Some of the faster paced games like Contra, Gunstar Heroes can't be done on the PC Engine. For the CD game some of the later game graphics are as good as some Snes games like Emerald Dragon, Ys 4, Legend of Xanadu 2, Seiyu Monotagari etc.
I'll post my own must have list in a moment. I'll mention a few titles that haven't been mentioned yet I believe.
Legend of valkyrie
Neutopia 1, 2
W Ring/Doube Ring
Double Dragon 2(borderline)
Dragon Slayer Legend of Heroes 1, 2
Spriggan 2(still good in it's own right, even though it's completly different from the first one)
Super Raiden(Not a Raiden expert but looks like one of the better versions)
Tenchi Wo Kurau(borderline)
Maybe 1 one 2 of the Valis games
As for a few of the ones mention. Here's kind of my own opionions on them
Coryoon, PC GENJIN SERIES CD DENJIN ROCKABILLY TENGOKU
and Magicial Chase.
Neither of these I found that great. You'll probably beat them in your first try and never touch them again. If you like the cutsey shooters Cotton is much better.
I'd probably replace Toilet kids, Ai Cho Aniki, Steam hearts with something else as there are so many better shooters on the system.
BAKUSHOU YOSHIMOTO SHINKIGEKI
This is a probably a sub par to average platformer and doesn't doesn't belong on a best of list for a system. there's about 3 or 4 other platformers I'd put ahead of this.
I would drop this one as the sequel is much better. Also the game has some programming problems where you can get stuck and not be able to go on kind of like with Arunumus No Kibi. Also the end of the game has stumped both me and Gaijin.
Probably replace Nexzr with Summer Carnival 93 as you get the both the full game as well as the 2 carnival modes.
Summer Carnival 92 could probably be dropped as a game that only has 2 carnival modes and not a full game on it.
Travellers is also kind of borderline as there a lot of RPGs that are much better on the system.