Well Hashirama is known to be a legend, and the manga has hyped him up from wayyy back - goodness just look at how many people crave the remains of his cells. It's like a parallel to the Sharingan.
I'm going to use assumptions to guesstimate what he had..
Mokuton - Well this is obvious. However some people actually tend to underrate Moktuon if you ask me. It's not all about smashing people with trees; it's basically creating a form of life. It's been used to track down people, induce sleep via pollen inhaling, control chakra substances like the legendary Bijuu, and I'm sure that's not the max of its abilities. Take heed that Danzo knew that using Hashirama's cells for Mokuton would be a fast and liable defense against a Susano'o arrow - the 3 hand seals needed for Izanagi was simply too much for him. Do not underestimate this deadly ability.
Elemental Abilities - Not proven but highly likely. Yamato (a heavily watered down version of Hashirama to be honest) was able to move entire areas of land high into the air and split them down. Using Doton, I'm sure that Hashirama could actually creature fissures if need be. Having water release only gives him more tools to use in combat.
Medical Abilities - If his healing abilities are truly on par with Tsunade's, or at least close to it for that matter, then there's no doubt in my mind that he was an extremely hard shinobi to put down. He could basically multi task by using hand seals for offensive jutsu while he healed himself at the same time.
The Sage's Body - Gifted with endurance, it's safe to say that he almost never wore out and that the jutsu he used were all on a massive scale. To be able to have landscape changing power.. he HAD to have this sort of chakra reserves. Seeing how he inscribed the multi shadow clone technique.. I'm sure that this legend could use it himself.
Sealing Jutsu - To be honest, being a close relative to the Uzumaki clan seemed to imply that the Senju excelled at this. I don't think Hashirama would be an exception either. Using scrolls in battle is probably natural for him. I can't expand on this too much but there are times where this should be vital in battle.
Yeah I know reading essay formats aren't very convincing, but if you just skim over what Yamato has done in the past and how Wood Release is used in general.. they all imply that Hashirama was a force that will not be forgotten anytime soon.
If we had to gauge his fighting style, I assume that he used Wood Clone feints (plus merging into the ground for extra surprise), outright overpowered the opponents with large jutsu, and used his versatility for any opponent who this did not work on >_> Inb4carnivorousplants