Opening Bid: Two Diamonds - 11-16 HCP
Long ago, we all played strong two bids, but in the 1960's we started playing weak twos, which were hated by the old-time players who didn't know how to defend against such blasphemy. It was especially bad for them, because there was no such thing as an alert! Well, today we all know what to do over an opponent's weak diamond call. Although the weak two spade call is still effective, the weak two diamond bid simply makes bidding easier for the opponents because you have given them a description of your hand while there is still lots of bidding room. It's not nearly as preemptive as two spades.
There's a better use for the bid:
Here are two hands, both with 13 points, and with the first one you would be quite willing to rebid 1NT after opening 1 and hearing partner bid a major. However, if you held the second hand, it would be better to simply open 2 immediately.
Because the opener does not have a 4-card major, your partnership should not use negative doubles. If an opponent overcalls your opening bid of 2 and your partner doubles, she means it for penalty, so PASS!
A 2-level response of either major, or 2NT, is highly invitational but not forcing. The opener should strive to find a reason to bid, but is not obligated to. Generally, the hand can be divided into two categories: 11-13 or 14-16, which will make your decision easier. Pass with most 11-13 hands and bid with all 14-16 points.
A response of 3 is not forcing, but is also highly invitational. Responder denies a 5-card major, and probably has support for diamonds.
Partner should raise your opening bid of 2 with support and a modest hand. The raise is neither invitational nor constructive... Consider it as preemptive.
All 3-level suit responses are natural and forcing. Responder has an opening hand and wants to be in game.
A jump to 4 is keycard Gerber. There are five key cards... four aces and the K, with three outside kings.
I can't tell you that this treatment is a popular agreement, as there are many uses for an opening 2 call, but it is useful with a strong club bidding system, and is similar to the 2 call, making it consistent with that bid and easy to remember.