What do you like best?
Reply is perfect for a small salesforce. If you have 2-3 salespeople and you don't want the training, upkeep and cost of Salesforce.com.. Reply is a great alternative for your organization. It's simple interface, 5 minute setup and helpful prompts make it very easy for an active salesperson to get in and get out while still never missing a beat with his/her prospects.
What do you dislike?
It took me a while to figure out how many emails I could send out. Because I was comparing Reply to services like Constant Contact. Then I figured out that Reply actually IS your Google Inbox. Emails are coming from firstname.lastname@example.org and not some dumb constantcontact.com address that gets blocked by everyone's spam filters. Once I figured that out, I was OK with only sending a few hundred emails a day out of my Inbox. My interactions with clients now are more natural, and it appears very real and authentic.
Recommendations to others considering the product
First, decide if you are Sales or Marketing. Reply should be used by the Sales person in your organization, not the Marketing person. Marketing people are there to work the top of the funnel, and get people "sales ready". Reply is made specifically to help those sales people who have sales ready leads, and need to close them.
What business problems are you solving with the product? What benefits have you realized?
You know, it took me a few days to find this feature in Gmail. When I loaded the Reply Chrome Extension, it added this bar at the bottom of the screen. I recently found that I could click and bring up all of my email templates. Now, when someone asks me a very common question or fills out a lead form on my website, I copy their email address into the clipboard, open a new email, drop in a template I've used before and I know works, and then paste their email and hit send. Super easy. Now I keep track of the emails that work (and result in YESes) and the ones that don't.