I don't live in Smithfield, but I've viewed places there over the past couple of years. I did consider it as a place to live. I'm sure some actual residents will be along to fill you in on their experiences.
As I see it, there are a few pluses, and some minuses. The negatives always outweighed the positives for me, so I never did move there.
Pros: Very close to the city centre. You can pretty much walk anywhere you'd want to go.
The Lighthouse Cinema. I've never actually ventured to it but I wish it was in my local area.
Negatives: Very close to the city centre. It's not all good. This is the north inner city. I always saw vagrant drinkers loitering around Smithfield on my visits there.
Certainly at the time I was looking it was relatively expensive to rent there. Rents have come down everywhere recently, but I expect it is still probably expensive.
I have heard the horse fair and the ice rink at Christmas be mentioned as negatives by residents. It's worth investigating if this is still the case, I imagine the exact location of your dwelling will dictate how badly the smell of horse ****e or the sound of loud, ****e music will affect you.
I ultimately went for Drumcondra, which is also convenient to the IFSC which can be walked to/cycled to/bussed to with ease. It's a little further out from certain parts of the CC for sure, but if you're closer to the Dorset St end there's not much in it, depending on where you're going. I see good value in rents here too.
If you really want to be in the middle of things then Smithfield might be the best choice for you, but personally I think it's overpriced and over-rated.