GTAIV is the single greatest piece of media humanity has yet produced. People don't appreciate it on the level it deserves, they compare it with culturally vacuous games that do nothing more than emulate the hollow experiences of toys and action movies. No other game encapsulates the depth of human culture the way GTA does. The in-game internet alone has more cultural depth than any other game. If you want to play an open world game that's mindless fun you've got Infamous, Prototype, Mercenaries 2, Crackdown, Saint's Row, Red Faction Guerrilla, Just Cause 2, Assassin's Creed, Dead Island, Alone in the Dark, Wheelman, Batman: Arkham City, The Saboteur & Rage. There's only one game for people who want a deep mature experience. RDR & LA Noire are much shallower because of the lack of technology in their world, you're left with newspapers and 2 primitive cinema clips in RDR and nothing at all in LA Noire.
the characters mostly unlikeable
Not a single one of the characters in the wire or the sopranas is likeable either. So what? Yusuf & brucie are 2 of the all time funniest video game characters. No other game series is as bold as GTA. You've got a strong muslim character, you've got full frontal male nudity and all sorts of other things. You've got parodies of cash4gold, alternative medicines, conspiracy sites, mail order brides, reality tv, celebrity stalking culture, sex tapes, the slave trade, anorexia, feminism, steroids, mmorpg's, diet pills, the ipad, chiropractic, fantasy sports leagues, poker shows, art industry, apple, online banking, car manufacturers, ringtones, protest sites, theme parks, homework helpers, animal cams, fantasy movies, old fashioned anti-technology sites, meat loving, vegetarian, eugenics, mysogynistic, hilarious cartoons, pregnancy sites, range of newspapers, fox news, outsourcing and immigration, lots of different conspiracies, politicians, the snuggie, drugs, photosharing, adoption, prostitution, all sorts of scams/spam, blogs (really in depth character parodies with goths, serial killers, jocks, sluts, etc.), skype, silly instruments, real estate, pornography, alternative medicine, paedophilia, cigarettes, beer, mexican doctors, police, modification of a variety of items (cars/toilets/appliances), radio, cults, farming, robots, gossip sites, lawyers, clubs, baby names, twitter, myspace, facebook, etc. These are detailed websites, not just single sentence jokes and it's a truly underappreciated gem.
People don't get that GTA is not a game about gangsters, it's a complete satire of society. I think a lot of the people who hate it are probably offended by some of these parody elements and have political/religious/whatever objections so dismiss them and focus on the other aspects of the game which are below par (mission structure & competitive gameplay).
The idea that games could be made that were as culturally relevant as films or anything else. That there was this huge audience of people who ... were very culturally savvy and culturally aware, but who were being fed content when playing games they found slightly demeaning. Dan Houser