Are there any differences between incendiary grenades and molotovs

Yes, throwing multiple Molotov Cocktails at the same area will result in stacked damage.

Molotov Cocktails do reasonably high damage and provide effects such as slowing, while being balanced around its price ($850) and easy-to-see visibility which make it easy to counter.

^{Discussion | Another discussion | Third discussion}

First of all, there are many differences attributed between CS1.6 and CS:GO. The most important thing to note is the engine; it's improved dramatically over the past 9 years (CS1.6 was released in 2003, CS:GO in 2012). Namely, CS1.6 uses the GoldSrc engine, which is a heavily modified Quake engine, and CS:Go uses the Source engine.

Second, CS:GO features drastically balanced gamemodes and weapons. Most notably, they completely changed the way Hostage missions worked previously in CS:S and CS1.6, and made it a lot more balanced for both sides. Some new weapons were added, and most of other weapons got a huge balance update (default pistols get a buff that puts them up to standard to other pistols, deagle nerfed).

Along with that, CS:GO also features a matchmaking system extremely similar to that of TF2, but it forms games based on a "combat rank", which helps to put similar players of similar skills in the same games.

Some other features are a complete UI revitalization, a more informative and easy to use buy menu, and an extremely polished user-friendly tutorial. Some minor things are the removal of flashlights (some servers have it with plugins), as well as getting rid of pre-defined loadouts.

Also included now are "weapon" skins, cosmetic variants of stock weapons that have no effect on gameplay but can do things such as track kill counts, be named as something else, etc.