Everybody who gets into music notation/composing knows Finale. It's the quasi industry standard, in its segment challenged only by Sibelius. I use both apps (and some other, more specialised software), and both have their positive and negative points.
I think the key for using Finale well, you have to make your own templates, and find your own workflow. That takes time, as Finale allows for more customisation than any other app in this field, it is very versatile; many give up on it during this process, but once you have "set up" the app for you and your needs, Finale shows its strengths. The core of this app is brilliant, I love entering notes real time by MIDI-keyboard (if you're not very good at it, you can first tap the rhythm with the hyperscribe-tool and then the correct pitches with the repitch-tool), the "engine" for those things is very good. Anyway the input-methods are great, if you do composing, the speedy entry (with MIDI-keyboard) is fantastic (you can play/try your music at the keyboard and Finale will only write down when you type together the rhythmic values). And yes, this app can create really beautiful professional scores – the point here is that you can really make your own, individually styled scores – nobody will see what app you have used for it. The web is full with plug-ins and additional fonts for Finale, so you have lots of possibilities to make your scores look personal. If you want to write avant-garde music, with advanced new notation, you nearly *have to* go with Finale – the only other app I can imagine for this is NoteAbilityPro. So, if you want to seriously get into music notation/composing and you want to invest time and money in your scores, Finale is a good choice.
If you're a music teacher or student and want to write some etudes or compose something from time to time, then I'd recommend MuseScore. You can try with Finale, but probably you won't get happy with it. I mean, if you just use Finale's default templates, you won't be really creating professional-looking scores (for example, the default font of Finale is Times New Roman :-) and you will still use a lot of time learning it. The best, but also the WORST looking sheet music I have ever seen was made with Finale.
If you do composing with more traditional notation (film music, pop music, most of the classical repertoire) I'd have a look at Notion. It has muuuch better sounds than Finale (or any other notation app), which is great if you do orchestration. It is easy to use and also has a good iPad app. Version 4 is just out, but no demo yet. Maybe also interesting for music teachers.
No, I haven't forgotten Sibelius: great for quickly making professionally looking scores (with beautiful fonts), only little learning curve. Good input methods, stable app, aimed more at traditional notation, but still flexible enough for most music. Actually a great app, however given the current situation with Avid, I wouldn't invest time and money in it at this point (for further details see my comment at MacUpdate's Sibelius page).
Back to Finale: there are negative points. The complexity of Finale, that is often attributed to its rich feature set, is in my opinion to a large percentage caused from poor design. I am really sorry to say it: the whole UI feels like a gigantic workaround. OK, there have been improvements, Finale is much easier to learn then it was 10 years ago, but basically, the interface in its core hasn't kept up with the addition of new features and basically remained the same for the last 20 years. There have been only small steps of progress to improve the interface, like in Finale 2012 the new Score Manager – still, these attempts are only half-hearted and make the user experience sometimes even more inconsistent. People claim "you can do everything with Finale" – well, yes, if you like tinkering. Because actually, Finale does have its limitations (and not only for very specialised stuff); but if you know how, you can overcome those with workarounds; and since Finale has great support, useful forums and tutorials, and (most importantly:) a huge user base, it's quite possible that you will find solutions quickly and easily.
But: a whole different problem is that the developer has adopted this "workaround"-style as the basic design concept of the app; this way the developer doesn't have to work on good UI design. It's like a bleeding arm covered with tiny pieces of band-aid, and as soon as there is some blood showing, one is putting another tiny patch on top of it. I feel there is only little will to improve Finale in this regard (keep in mind there is also a sort of "Finale-help-market", with many people earning money by giving workshops, seminars, classes of "how to learn Finale"). It's funny, if you don't know where to find or how to change something, don't even try – check the manual or Google: otherwise you will never find it. For us Mac users that feels strange, as we are used to well designed software, where you can find solutions by thinking logically. But well, don't try that with Finale, you'll just waste time…
Resulting from that developer's mindset, the updates are often disappointing. Some of the new features are just beta-style implemented, often just new workarounds… Bugs don't get fixed, etc. etc. etc. At least, MakeMusic has changed its policy of throwing each year a new version on the market. But in the meantime I have given up hope for any major improvements, because somehow everybody who is still with Finale has arranged him/herself with the app and can live with it.
Well then, is Finale worth the $600? To be honest, I don't think many users have paid that much for the app. Most of us got it from an institution or with educational discount, or through a competitive upgrade. I mean, if you buy Notion 4 (now on sale for about 60$), you get Finale for 130$. And maybe you stick with Notion anyway… And well, there is some $50-hardware (M-Audio mini-MIDI-keyboard for example) that have an older version of Sibelius included, with which you qualify for a competitive upgrade of Finale too. So if you have time, I would recommend to look for a good deal, can save you a lot of money. I'd recommend NOT to use any of the "smaller" versions of Finale, like "Allegro" or "PrintMusic" or whatever. Since you will almost certainly need to google to get some help using Finale, and many useful (some even necessary) workarounds and also tutorials etc. probably won't work with one of the "little" versions.