Tamiya... I am on my forth Tamiya-based semi build. Overall, things go together fairly well, their designs are tried and true. With that, I have some rants...
• Batteries: Do the good folks at Tamiya know that 6-cell NiCDs are no longer in vogue? I don't think so. Granted, there are a couple of lipo pack that do conform to that same form factor, but I don't own any of those packs. I hate having proprietary packs for specific RCs, and run 3S 3ah shortie square packs for most of my rigs, which do not fit in the Tamiya battery trays. Thankfully, there are other places to stuff batteries in their rigs.
• Phillips screws. They are good quality hardware, and thankfully, no slotted, but still, hex hardware would be better.
• Transmissions. The best that can be said for them is that they do work. My biggest gripe is that they are a pain to assemble, especially when the two axles and gear linkages go together, you need six hands. My other gripe is their size, these can be made a lot smaller and compact today. I understand that changing an existing design, especially one that works is costly, but sometimes it is just time.