I'm not going to beat around the bush here, Heat Guy J is excellent. It is the kind of series you come across every once in a while where you know next to nothing about it and on paper it does not sound that great but once you watch the first few episodes it hooks you in and provides hours of solid entertainment. The reason i liked it so much is 2-fold. First, it has got some great characters, and some really memorable characters: my personal favorites are clair leonelli, the head of the cities biggest crime family , and Buma, a sword-fighting werewolf who not only looks cool but has one of the most entertaining sub-plots in the series: and second, the story is extremely well told and is an interesting tale touching on many different themes and as a piece of mafia/crime fiction it could hold its own against many similar tales. The character designs are excellent across the board with one exception, Daisuke's brother Shun could easily pass for the twin brother of Integra from Hellsing, and the dub is extremely good here. a lot of dubs are poor but here it is well casted and all the voice actors do a great job and fit their respective characters to a tee. The story really is the star of the series in my opinion . Once the main plot really starts to develop it moves at a great pace and there is not that many episodes i would consider filler. There are some great twists in the second half of the series and some of them really throw you off guard. The story deals a lot with the theme of revenge and to be specific the idea of taking revenge, versus letting go of your hate. Personally i find the mark of a good series is that when you are not watching it you are thinking about and trying to figure out whats going on, and Heat Guy made me do this a lot. The animation is also excellent and mixes in some CG/3D effects into some sequences and these sequences look good more than they don't. The action is fast paced and well animated.
Overall this is an excellent series. The main characters Daisuke and J are fun to watch and have a great partnership and most of the support characters are equally if not more entertaining. It's got a great story and excellent animation and voice acting and i would reccomend it to any anime fan.