Pros:
* Matchmaking: Being able to simply choose some basic settings (deathmatch, team deathmatch, CTF, etc.) and hit one button sure is an easy way to get in and get playing. Infinity Ward promises that matchmaking will get you playing with others of the same skill level, meaning fewer instances of landing in games with tournament-level players who can pick you off with a handgun from a football field away. This should also put you in games that your computer has a strong connection to, so that you don't have to hassle yourself with trying to look for a game with a low ping that will stutter the least because of a bad connection.
* Lower Barrier to Entry: For the hardcore crowd, scrolling through a server browser might seem like a cakewalk. But for a casual gamer who perhaps isn't used to doing this, matchmaking will remove the daunting task of wading through hundreds (if not thousands) of server listings trying to find a game that is playing a certain map with an acceptable ping that isn't full or empty.
* Fewer Cheaters: This might not be 100%, but putting the responsibility of weeding out cheaters on automated systems maintained by IW is a very appealing prospect. It's even more appealing when considering that the alternative is hoping that someone is hanging around your server with the power to kick or ban modders.
* Party System: Anyone who has played Halo 3, Uncharted 2, used Xbox Live's party system, or played any number of other more recent releases on consoles knows the beauty of parties. Easily moving from game session to game session with a group of friends at the push of a button is immeasurably more handy than having to share a game name or IP address with your buddies or clan members.

Cons:
* No Mods: Perhaps the greatest appeal of PC games lies in the mod community. Beyond the appeal of higher resolutions, keyboard and mouse control, and lower prices (although that isn't the case with Modern Warfare 2), mods can help to greatly extend the life of any PC game. Shooters, in particular, are often the recipient of grand remakes and enhancements by way of modders, whether that come in the form of new weapons, redesigned HUDs, and additional maps. IWNet does away with all of this, as servers can no longer be run by individuals who opt to use modded content.
* Lag: Try as it might, matchmaking isn't a perfect system. While it ideally will find you a game with both players of the same skill and a low ping (giving you a lag-free game session), you can't count on it to always pick out a server that will give you the most lag-free experience possible. * Downloadable Content: With user-made maps out of the equation, you're stuck with what maps ship on the disc and any subsequent releases by way of downloadable content. This might not strike console gamers as unusual (unless you've gotten a taste of the world of mods with Unreal Tournament 3 on PlayStation 3), but for the PC crowd that are used to getting an unlimited amount of uncensored, unmitigated content for free, this is a massive departure from the norm.
* Matchmaking: As nice a convenience as it can be, the time that you'll sometimes spend trying to find a match by way of matchmaking is time that could have otherwise been spent playing the game. (Perhaps this will be improved, but any Halo 3 player knows the horrors of waiting many minutes in order to match up with a group of other players, especially when you're in a group yourself.) Gone is the ability to denote a server as your favorite. Doing that would allow you to immediately jump into a game with a familiar map rotation and set of rules that is frequented by people whom you've played with in the past but don't necessarily wish to befriend. Communities form on servers. With IWNet, that can't happen in the same way as we're used to seeing in FPS games on PC.
* Griefers: If you opt to play in a private match, you'll be given free reign over the game session you're in. But players are powerless to do much more than mute a player and leave negative feedback when playing on an open, public server with someone acting like a jackass by screaming into their microphone, interfering with the game, or whatever else they can think of. Anti-cheating measures can't do anything about this, whereas playing in the traditional type of PC server -- where player admins capable of kicking/banning players could be lurking on a server -- could lead to that player being banned.

What this really comes down to is a matter of choice. IWNet eliminates much of the choices and freedom that PC gamers have enjoyed for years, and it's also removing one of the greatest advantages to playing games on a PC in mod support.

The appeal of this for Infinity Ward and Activision is very obvious: It'll make things much easier for the average to get in and play a game; it may help to curb piracy by checking that you're using a legitimate CD-key (though Infinity Ward claims matchmaking won't have much of an impact on piracy); and it incentivizes downloadable content to a market that could otherwise turn to an unlimited supply of free, community-made DLC.