Yeah, micro-transactions are actually a great model when used on cosmetics and stuff like that. It's the standard model for most MOBAs, and it works really well there. League of Legends is probably my favourite game, and I know people who have played for years spending from $0 to hundreds of dollars, with no competitive advantage either way.
With all three types of additional paid content, it's too diverse to give a generic good/bad answer here. Sins did fairly well with both expansions (Fortification, Rebellion) and DLC (Forbidden Worlds, Stellar Phenomena) models, while also having some on the less-great side (Diplomacy). Cities: Skylines as well. They have really robust expansions, with a lot of the functionality coming through free patches for people who don't buy it, and they've done cosmetic DLC/microtransaction stuff where for a few bucks you get a couple new building models and skins in different styles. For these, they've even contracted individual modders to do the work and then paid them a certain amount of the revenue, which I obviously think is a fantastic model for a business to follow, and think they should contact us at ThrawnsRevenge@gmail.com
anyway, my bottom line is, while a lot of this stuff may seem like it's overpriced, there's a certain understanding with a lot of these models where you go in with the understanding that part of what you're paying for is for the company to continue being able to support the game. Some would say easy cash grab, others, like myself, would disagree with that characterization. It's a lot more dependent on the company, and a lot of that comes through in the quality of the base games as well. With Colossal Order and Cities: Skylines and SoaSE, you can tell it's a company that really cares about the game it's making and uses the DLC, expansion and microtransaction models to support that in a pretty transparent way. There's other companies, like EA, or microtransaction-based freemium games which are usually a lot more obviously just in it for cash grabs.