Starbow is a fan-made expansion to Brood War, built in the SC2 engine. It intends to recreate many of the good gameplay aspects of BW, while using units and spells from both games.  

Notable Features:

- Brood War economy (rewards taking expansions).

- High ground advantage (units attacking uphill have a 50% miss chance).

- Combat tends to last longer and occur over a larger area, compared to Starcraft 2.

- More positional play.

- Retains Starcraft 2 mechanics (e.g. unlimited selection).

- Balance is generally based on Brood War.

- New options have been added compared to Stacraft: Brood War. Robo openings against Zerg, Bio openings against Protoss. Beating a Zerg in a longer ZvZ without mutalisks. etc. This allows new players to explore more options and even catch more traditional BW players off guard. The classic BW strategies that were most interesting are still viable.

Starbow is aimed at being an expansion to BW built in the SC2 engine. It isn't trying to be a better SC2 like most SC2 melee mods do. Its built on BW fundamentals instead of SC2 fundamentals. The resources, map design (ported from BW for the most part), rush distances, and build times are a lot more reminiscent of BW.

Armies feel more spread out, and fights can happen over much larger space, despite armies generally being lower supply due to the lower economy. Starbow also puts a lot of emphasis on micro being a pretty big factor. Things that are anti micro generally get developed out of the game.

Fundamental changes to units were made as well to make fights more micro-able than their SC2 engine counterparts. Fights tend to last longer.

Here is an overview of the main differences between BroodWar and Starbow: