What are the weak points of Pass amps and pre-amps ?

Pass are great amps in the right system or personal tastes. I jumped on the bandwagon several months ago and purchased a X150.8. My 1st impressions were, powerful,  dynamic,  very nice looking amp, clean crisp sound but lacked in midrange richness. I changed tubes in my preamp to help with some midrange energy I was experiencing even with Sonus Faber Olympica iii.  It helped but overall I couldn't warm up to the amp. Hated to sell and wanted to like this amp but just couldn't get it to work in my system.  YMMV. Overall it's a very good amp and compared to pricier products it's a no brainer. Extremely well built and affordable.  

I've bought and sold a number of amps over the years.  Pass is one of the few I regretted selling in hindsight and the only one I reacquired, moving up from the INT-60 to the INT-250.  I thought it might be overkill for my 100db efficiency speakers, but the data retrieval, dynamics, soundstage, bass grip, etc. is excellent in my system, my room and to my ears.

My experiences with pass labs gear has been very positive… well designed gear using quality parts , reliable and long lasting in terms of time and viability. I prefer the sound of the XA series amps for most music, leans to the right of neutral. the X series amps I find more neutral sounding and better for playing loud hard hitting music..
I am now using a Pass XP22 line stage after trying the XP12 for several months, my first foray into SS pre’s after decades of tubes and passives. I went from an XA25 to a SIT3 and enjoying low powered SET like sound. I like the First Watt amp sound the best so far, but proper matching and sensitive speakers is a must to get the most from it.
Someday I would like to try the XA100.8 amps..  but right now this combo is quite enjoyable..
Price wise, I find Pass gear to be a good value, there are some amps out there that have $90k in the case work and $5K worth of parts and manufacturing.  Pass is solid gear for the money.
As with most things audio.. get what sound best to you..