TL;DR
Japan’s tech tree is unique and very fun, especially at the top tier, but it faces issues with BR placements, armor, missile performance, and lacks sufficient CAS, SPAA, and light tanks at high levels. Potential improvements could come with new additions or a subtree if Gaijin gives it more attention. I haven’t regretted grinding Japan; if I were to start again, I would play Japan first.
Long explanation
In terms of air, Japan is rather unique up until the Cold War, where options drop significantly. If you are looking for top-tier planes, the F-16AJ is a lot of fun (with some amazing camos) and will be followed up with the F-2A or F-2B, which could come with some unique capabilities and AESA. The F-15J and J(M) are also good with AAM-3 (a better AIM-9M), but in terms of ARH, they will basically stay the same as America. Gaijin has done a rather poor job with the AAM-4, and in most situations, it is worse than the AIM-120B, at least it was the last time I tested it.
Generally, the F-15J and J(M) are very similar to their US versions. They have the AAM-3, which is essentially an AIM-9M with better G-load performance. Other than that, they are about the same. The F-15J(M) does have the AAM-4, but as mentioned, the AIM-120B is usually more effective. There is a more advanced version (AAM-4B) that could come with either the F-2A/B or a later F-15J, but I have little hope for the AAM-4B being any better than the AAM-4. A subtree that could add the F-16 or JAS-39 would be beneficial, especially for CAS.
In terms of ground, Japan is very, very different from most other nations. They usually have very little armor with rather okay mobility and firepower compared to most other nations. At top tier, they are very fun (and very scary if played right). The Type 90s have insane mobility and reload, allowing you to get away with some daring plays. Type 10s are similar with better firepower, reverse speed, and optics. The issue with them is the lackluster armor; most shots to the turret will penetrate, and you have virtually no side armor. Autocannons have no issue killing you in most situations.
There is little future for new tanks after the Type 10s unless Gaijin adds a subtree (which seems likely). If so, it would freshen up the Japanese top tier in general. Potential additions range from the 2RI/2SG to T-84 Oplots, F-16s, and JAS-39s. It’s in a situation where it could be much better than it currently is if Gaijin gave it more attention. But regardless of the current and future, it is still a VERY fun tech tree.
