"Metroidvania" is a term used to describe a sort of exploratory 2D platforming game. It comes from the original games of the Metroid series and some of the middle-era of Castlevania games (most notably "Symphony of the Night", which is what primarily gave birth to the term).
The most defining feature is usually the world. Rather than have set stages or a world map, the entire game takes place inside one giant map, which you must traverse about. Not just any map, but typically a very complex map filled with all kinds of secrets. The map is typically divided into sectors, more in an aesthetic fashion to denote that the denizens and dangers will be different. Sometimes you have teleports to assist you in travel, but other times you just have to remember where to go in the map.
There's various elements at play in the exploration. There's typically tidbits hidden in spots, or puzzles that have to be returned to when you find appropriate equipment. The exploration is also non-linear - your limits of progression through the map are by various tools or powerups that you need to acquire, but the order in which you must acquire some of these tools is not set. And in many choices, there are many paths to get those tools, or even get past obstacles without those tools.
A very popular element of these games, especially in the Metroid franchise, is the concept of "sequence breaking". Using special tricks or otherwise mastering the utility of your basic abilities, you can sometimes access items and areas far earlier than the game expects you to.
As far as I know, Metroidvania games have always been 2D platforming games. Aside from the elements of exploration, the actual gameplay of Metroidvania games vary widely.
Aggro as a term originated in MMO's, but its usage has spread considerably.
Originally it was coined to describe any creature who would attack you on sight. So an "aggro" mob was one who would attack without being provoked, as opposed to one who wouldn't attack unless you attacked it first. The related usages here are "aggro range" or "aggro radius" which is the distance at which the mob will attack, and "aggro chain" which is whether or not the mob will bring his friends along, even if they are outside of normal aggro range.
As the games evolved "aggro" became the state of being attacked. If you were being attacked, you "had aggro", and if you did too much damage to something and it started attacking you instead of someone else you "stole aggro". If you did something stupid you could have "too much aggro" which meant too many things were drawn to attack you.
In your example, he's saying that the unit AI can be exploited because they don't chain aggro, so you can move into their aggro range, and individually "pull" them from their groups and eliminate them one at a time.
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I think there's a difference between the dry definition of a port and the thing that people complain about.
The term "a port of a game" means a game was developed for one set of platforms, and it was later released for other platforms. Technically, a game released for multiple platforms from the get-go - such as Crysis 2 you have mentioned - shouldn't be called a port.
But that's not what people complain about. A game can be a port from its version on another platform, and still be a great game which was carefully ported. What people really complain about are games that exhibit elements not appropriate for the platform they are running on; unfortunately, this is a common occurrence with ports, hence the connection.
The problem isn't really exclusive to ports - a port may be a good port (modified to fit the new platform perfectly), while a non-ported game released on many platforms may simply work better on one platform vs another. The truth is, though, that many game today are designed with consoles in mind, and unfortunately their PC version (whether a port or a simultaneously-released version) is inferior because they are not properly adapted.
Common examples of things not properly adapted are UI elements - e.g. where mouse navigation is lacking while keyboard navigation is fine; aiming - where in consoles FPS often have auto-aiming mechanisms that should not appear on the PC; driving - where the accurate gamepad control does not have a parallel in a PC keyboard; etc. One of the biggest ones is something a little less obvious, and that's performance - a poor "port" might have poor performance on the platforms it was not originally designed to work with.
EDIT I've recently found this nice piece listing problems or missing features that plague PC releases of console-oriented games nowadays. Although it specifically bashes some select titles, it does mention problems that I've seen in many recent games, and I thought it's worthy to include the link here.