I'd say Japan is kind of a mixed bag, but leaning more on the 'good' side. Their main downsides is lack of armour protection on their vehicles, lack of good HMG's & GPMG's and somewhat subpar infantry.

The Japanese tanks have more firepower than they're given credit for, especially in recent updates. They're guns are capable of dealing with the vast majority of enemy tanks (Their Type 5 75mm guns with the Type 5 Otsu APHE shell has around 180mm of pen at close range iirc.). But they of-course lack armour compared to their opponents and also lack MG's for anti-infantry, usually just one hull mounted and/or AA mount. They also have relatively low MP cost to compensate for their short-comings though.
I'd recommend primarily using their larger tanks (Chi-Nu, Chi-To, Chi-Ri etc.) as TD's. Pull them up to destroy enemy armour and pull them back as fast as you can, since they won't have the armour to deal with the inevitable counter attack. And I'd recommend against doing tank pushes/rushes unless you KNOW for a fact the enemy doesn't have a way to effectively defeat it. Use artillery and infantry spam for rushes.

Like I mentioned before, Japanese Infantry is generally subpar, however they do have some good specialized infantry. They have a good AT Rifle (Probably the best in the game), god tier mortar infantry as well as the Kamikaze.
The use and usefulness of the AT rifle squad is self-explainitory, it's just good at it's job if you get it in the right spot.
The Type 89 Grenade Discharger mortarman is best used early game and in conjunction with a ammo box. It can and will decimate enemy squads and take out the early MG vehicles the enemy will use. Just make sure it's in a spot with good cover and within range of the enemy (It has 110 range iirc).
Kamikaze infantry is pretty simple to use, just make sure you don't just charge them out in machine gun fire. Use cover and shrubbery to cover their advance and only try to go for vehicles/implacements with minimal infantry cover. Otherwise you'd just be wasting MP.
The rest of their specialized infantry is just par-for-the-course stuff.

In terms of their infantry squads they just lack the firepower of other nations like the USA or Germany. Japan doesn't get semi-automatic rifles or GPMG's and their regular squads don't have good accuracy (The Type 99 LMG is pretty good though.). But they do come in larger numbers than other nations, even more than the USSR. Oh, and of-course they ALL have grenades, so grenade spam tactics are really good with Japanese infantry. The best ways to use the Japanese infantry is to just rush enemy positions and cap points with waves of Banzai Chargers and/or Assault Sections (Ideally with artillery support) and spam grenades like the second coming of Christ is coming in 2 minutes. If you manage to take it use Regular Infantry or better to hold it.

Japanese artillery is good. The Type 97 150mm mortar is great, the Type 96 150mm has WP shells and the Type 4 200mm and the Ha-To are one-shot wonder meme machines. Isn't any specific trick to using Japanese artillery that wouldn't apply to all other nations. Only real problem is that they don't have MLRS artillery like the Calliope or Katyusha.

Would write more detail but got to go to work so I'll just post what I got down here. May post more later.

TL;DR Use tanks wisely, rush and grenade spam with cheap infantry, make full use of specialized infantry, artillery your enemy to kingdom come.

i recommended for artillery to cover fire the kamikaze assault group to destroy enemy armours, after that push the remains enemy with the main forces or use 3-4 banzai charges so they can cover the kamikaze assault group