I've been playing a silly, fairly bad phone game recently which is ad supported, and, unlike most others I've played, it doesn't let you buy a no-ad version. Thus, I've been subjected to lots of ads, and the overwhelming majority are for a small set of other Android games. (The ones that come to mind are Clash of Kings, Blades and Rings, Forge of Empires, Ghost Town Adventures, My Singing Monsters, Immortal Conquest, Idle Heroes, Empires and Puzzles, Brutal Age, Gardenscapes, and Endless Frontier).
First, a disclaimer: a game being "bad" is pretty subjective. Obviously, some of the games I discussed are enjoyed by some people. I think my notion of bad is made most obvious by what I say below -- but, to try to put it specifically.
Bad games are:
-> games that are basically indistinguishable from similar games in the genre (they offer nothing new)
-> games where your enjoyment is interrupted frequently (some idle games are ok, because they naturally let you put them down and check in later, and have nice chunks of things you can do when you do check in. But a game that really wants to be a sit down game you get into, which instead makes you either pay up again, or stop playing, is bad)
-> games where the primary mechanic is to wait a day or pay money, especially when they are competitive. The latter is called "pay to win" and is widely derided. Even when they are not competitive, this means that the only thing being tested is your patience. There should at least be some strategy.
-> games that are basically indistinguishable from similar games in the genre (they offer nothing new)
-> games where your enjoyment is interrupted frequently (some idle games are ok, because they naturally let you put them down and check in later, and have nice chunks of things you can do when you do check in. But a game that really wants to be a sit down game you get into, which instead makes you either pay up again, or stop playing, is bad)
-> games where the primary mechanic is to wait a day or pay money, especially when they are competitive. The latter is called "pay to win" and is widely derided. Even when they are not competitive, this means that the only thing being tested is your patience. There should at least be some strategy.
-> games that are a previous game (e.g. candy crush, that game where you matched gems etc) with some thin new skin around them to make them look new.
Based on the advertisements alone, they look pretty awful -- but I've gone and tried a couple that seemed tempting. My Singing Monsters seemed like a promising and cute game, but it's so aggressively monetized with IAP and ad-driven rewards, it's not really enjoyable.
The ads for the other ones look pretty bad for several reasons. First, most of the time, the ads contain almost no actual gameplay footage -- rather, they have cinematic trailers that are, at best, misleading as to what the game is about and what it's like to play.
Second, they often advertise features that barely seem worth mentioning -- immortal conquest says "outplay others with alliance!" Ok, it's a strategy game, and you can make alliances. That's not that cool. Finally, a number of them just show off busty 3d rendered ladies, which, frankly, is an appeal to the lowest common denominator. Chainmail bikinis may have sold me on some fantasy books when I was 14, but, seriously. They imply the game has about as much substance as the armor itself.
Others look visually exactly like Zynga games, which makes them seem like they have no artistic vision.
There's a ton of games that seem to be driven by the same mechanics as existing games (e.g. you match candies on a grid to make them go away, and then things drop, and you make more matches) but they are "new" and "better" because they have different cartoon animals on the screen.
All of these games are "Free to play." Given how aggressively they are advertising, that means they must all be heavily driven by in app purchases and other ads. So, I think it's inevitable that these games will not be any good -- they'll just spend their time trying to tempt me into buying in-game gems/coins/whatever, in order to lure the next suckers in.
In addition, being uselessly similar to an existing game is a feature for these games, because they are likely to get people who liked candy crush or whatever to at least try them. Even if the vast majority don't end up playing and paying, they only need to get a few people to break even.