This post is somewhat old but I will give my two cents anyway. I've lived on Superior & 15th, 3rd St. & 14th, and currently I'm around 3rd St. and 15th.

Pluses:
Close proximity to Lake Superior, the Lakewalk, Leif Erickson & the Rose Gardens, as well as possibilities for beautiful views. Going the other direction, you have access to one of the best trails in Duluth (in my opinion) with Chester Bowl - this can be about a 4.5 mile hike if you take it all the way up (near CSS) and back. If hiking/trail running isn't your thing, there's always the Anytime Fitness.You're also very close to downtown.

Location is close to a mediocre grocery store, a Walgreens,a Jimmy John's and a Great Harvest Bakery/Sandwich Shop, an Ace hardware store, and auto parts shop, Alonzo's Book Store, the Chester Creek Book Store/Antique store, Positively 3rd Street Bakery, Burrito Union, a couple laundromats, a small liquor store, and The Farmer's Market which runs spring-fall on Wednesdays afternoons and Saturday mornings. You're also fairly close to other businesses and the London Road business district (including about all the fast food options you could need, too). Unfortunately the space that used to be a "mini mall" housing various businesses was bought up by CVS, so another pharmacy will go up across the street from Walgreens within the next year or two. It's too bad because it would be a nice place to see some small businesses or a deli take up residence. There's also a bike/ski shop, a couple hair salons, a dentist, and some other small businesses nearby. There are gas stations on 12th and 4th or down on London Road.

Minuses:
In terms of this neighborhood's appearance and how "pleasant" it is, it varies block to block. There are nights where the neighborhood is extremely loud. A group of teens screamed and fought for about 20 minutes a couple of nights ago and it's incredibly loud. The street traffic is loud in some areas too - lots of cars missing mufflers. I have some very shady neighbors and many who have no regard for people trying to sleep, but I also have some really great and friendly neighbors too. A fair amount of college-age kids move into this neighborhood at the beginning of the school year. I've witnessed a fair share of domestics, police calls, and fights/ruckus just within or outside of my small building alone. 

Parking can be a real pain in the butt if you don't have off-street. Lots of these college kids don't yet have a lot of experience parking their cars up or down-hill, and as soon as the school year starts, it's harder to find anywhere to park- especially in the winter, as another poster commented. Invest in a good set of tires or you'll be screwed when parking up the hill with ice and snow involved. 

Overall it's a good neighborhood, but it's nothing fancy or even very special to look at. Parts of it are "iffy" but I've never really felt unsafe. It's definitely several steps up (in safety and appearance) from the central hillside. There are some good views of the lake and rent isn't bad. I've always paid around 350 with roommates or 550-600 on my own in this area, and it really is the best neighborhood for convenient  access to lots of things - it'd be a good area to live if you don't have a car, for instance. Buses run on Superior St. and 4th Street. 2nd & 3rd are one-ways and make any type of transportation nifty, but they're also loud, as they're ambulance lines. Watch out for traffic when entering Superior Street from Jefferson, and exercise caution entering 4th from any of the avenues, up OR down - the visibility is awful because they allow cars on the street to park right up to the street corners of the avenues. 

Good luck.