There should be a new gold standard for judging the success or appeal of any new music service. It's all about ease of use, intuitiveness and general user-friendliness. In short, does it just work, without you having to think too much about what you're doing and how you're doing it.We've been hearing some rave reviews about Spotify since it launched earlier this month. It offers streaming music from all four major labels, as well as indie distributor The Orchard and rights body Merlin. And it comes in a choice of free (but ad-funded) or subscription-based (but ad-free).Having spent this afternoon playing with it, we can confirm that it fits our 'does it just work?' criteria, offering a clutter-free way to discover and listen to music. Read on for more thoughts and screenshots.The first thing to say is that Spotify is a PC/Mac/Linux desktop application, not a website. That's an interesting decision given the web-based competition from MySpace Music, iLike, Imeem and all the rest. However, the download is mercifully quick, and once installed it's quick to get up and running, and doesn't seem to be a CPU-hogger.It looks quite bare-bones when you first fire Spotify up, with a Home screen containing a few 'What's New' albums, and a tab to bring up some Top lists. One of the impressive things about Spotify is that a lot of its features are buried beneath the surface – it's never cluttered, although that does mean you have to do a bit of playing around to make the most of it.Clicking on an album takes you through to its dedicated page (right), with cover art and a list of tracks. Double-click on a track, and it starts playing. Easy-peasy.There's also a New Playlist button on the left-hand side of the screen, which lets you create, yes, a new playlist. Type in its name, and you can drag and drop albums or tracks into it.I can see myself setting up some permanent playlists, and then having one free to just drag a few albums into at the start of the day to leave playing. The option to set playlists as 'collaborative playlists' by right-clicking on them and choosing that option is intriguing. They let you create a shared playlist, editable by as many friends as you like.The Top Lists screen (right) is also deceptively simple in its look. In fact, it's not that impressive when you first look at it, with a list of ten popular tracks and ten popular artists. But you can click on Tracks or Artists at the top of the page, and change them to Albums if you want.And then you notice the little button saying 'Everywhere' beside each of them. Click on those, and a drop-down menu appears letting you organise the screen by different criteria.For example, you can check out the top ten current artists, tracks or albums in the UK only, or further afield (who knew The Kinks were so popular in Estonia?). You can also change it to reflect the most popular stuff 'for me', which presumably offers up personalised choices based on your play history.While using the app, the artwork for the currently-playing track remains at the bottom left corner of the application, allowing you to quickly pause, skip or rewind. This is similar to the currently-playing bar on Nokia's Comes With Music application, which we liked last week.To mine the depth of Spotify's catalogue, you need to use the search bar at the top of the screen. In response to your query, you get a list of suggested artists, albums and tracks (right), all of which can be clicked on to explore further, and in the case of tracks, double-clicked to play (or dragged to your playlist). Again, it's clean and simple.The catalogue seems pretty deep – unlike Comes With Music, Spotify DOES have some Oasis and Franz Ferdinand albums, although Arctic Monkeys are still elusive. There's some pretty obscure stuff too (to UK ears) – perhaps due to the service's European nature.There's also some neat shortcuts (we admit, we read the online FAQ and found out about these), so you can type in genre:hip-hop (or something else) to search specifically for hip-hop, and type year:1977-1982 (etc) to search by release date.Another neat feature is the openness of the Spotify application. Right-click on any track, and you can send a link to it to any friend via email. There's a choice of a direct Spotify link, or a traditional http link – which you use depends on whether you're sending an email or posting the link on a webpage.And then there's the Radio screen (right), accessed via a link at the top-left of the Spotify app. Here, you choose a timespan at the top then click on a bunch of genres, and you're served up a personalised playlist. So if hard-rock-techno-funk from the 1950s is your thing…All in all, we're hugely impressed, despite our initial niggle over having to install a desktop application. There's still a downside to that if you're hoping to use Spotify at work, and you have a particularly restrictive IT policy.So what about those adverts? They're audio ads that suddenly pop up in your playlist – the first one we heard was for Sainsbury's. They're pretty unintrusive, particularly within the context of a streaming service.In short, it seems those rave reports were on the mark. Spotify is a service to watch out for, particularly as it fleshes out its features in the coming weeks and months.