I realized after a while that how good you are at a game really changes your perception of what is 'fun' regarding the game. While I can only speak in terms of music games, I'm pretty sure this is applicable to any genre (and in fact any discipline or hobby). At the risk of alienating every reader of this, I'll stick to the genre I know.
For one, you realize a lot more thought went into certain things you overlooked
before and how other things actually have much less thought to them. It's the difference between why Lindwurm, Valanga and Vairocana are awesome charts in Reflec Beat and HAERETICUS is anything but - the difficulty is literally thrown in for difficulty's sake because you cannot figure out why this person out there decided that this should be a chain, that should be a hold and this should be a double. If the rationale fits, the notechart becomes an extension of the song very naturally; you can understand the notechart as quickly as you understand the song.
Another example I can think of is how all the relatively noob people at IIDX all go "wow Beastie Starter on IIDX is an 11 this is easy, this is boring stuff" and I see the KACA 2012 IIDX representative comment that it's a really good chart and I tend to agree. Another example is Just Awake on Jubeat and how I can remember Jovian immediately calling it out as a lazily done song and being shot down because it was apparently "fun" - in the sense that you had to press lots of buttons.
For most people in music games they look at one thing first - difficulty. Anything that doesn't fulfill this requirement is a terrible song. You can see the examples everywhere in music games - everyone rushing for Evans on jubeat just to score a C, some kid proudly declaring that he's 'youngest in SG to AAA deadlock' and every other person around looking forward to spam lvl 10+ songs, and people thinking of every song in IIDX as a 12 ("is it me or is this easy?" when you're barely passing 11s on Easy Clear? seriously?)
Once you start clearing all the actually hard songs, however, you start to understand the subtleties of the difficulty and the creativity behind it. All the hardest songs in IIDX are hard for very different reasons - Mei for the legendary slow-to-fast scratchspam, Plan 8 for that highly note-intensive scratch ending, Nageki for its doublescale near the ending, p†p for the hold notes and sudden trills at the ending, DIAVOLO for the ultra fast staircases, Himiko for the entire slow ending. All these have a lot of thought into them to make them difficulty but NOT insanely awkward, where the player can understand how s/he's being challenged by the chart creator in a manner that isn't "I want you to P1 scratch with your right hand" or something equivalently stupid.
Then there're somewhat iffy things like Timepiece Phase II CN Ver where there's a random measure with a hold note on 4 and a 3-5 jack if I remember correctly. It basically screams "I want you to random this because I know it's stupidly hard to hold the middle note and have jacks on the two notes just beside". If you can understand how a chart is supposed to work AND STILL disagree with the creator on why it's bad, the chart is irrevocably bad. Of course this understanding can't be superficial like "fast streams are bad" or other forms of arguments derived more from one's lack of skill than from one's capability. Once again, to rage at HAERETICUS again, it's the difference between the hold notes in Valanga and the hold notes in HAERETICUS - you cannot imagine Valanga without the hold notes because sufficient thought went into it that you imagine the holds as integral to the notechart. HAERETICUS not so.
Ultimately though being good at the game changes your perspective of difficulties and fun - you start to understand the motives and mindset behind certain charts. You can start to see how certain things fit in together naturally (this may be circular logic but nvm) and other things are sloppily thrown together. It may seem somewhat like a case snobby connoisseur-ism, but I do stand by the idea that you should be good at the game before you start criticizing whether something is good or bad, especially against someone else much better who expresses his/her opinion about it.